DE112013007781B4 - Light emitting element, light emitting device, display device, electronic device and lighting device - Google Patents

Abstract

Light-emitting element comprising:
a first electrode,
a first light-emitting layer,
a second light-emitting layer, and
a second electrode, wherein the first light-emitting layer is arranged between the first electrode and the second light-emitting layer,
wherein the second light-emitting layer is arranged between the first light-emitting layer and the second electrode,
wherein the first light-emitting layer comprises:
a first phosphorescent compound,
a first host material, and
a first organic compound, the second light-emitting layer comprising:
a second phosphorescent compound, and
a second host material, wherein the first host material and the first organic compound are suitable for forming an exciplex,
wherein the light emitted by the second phosphorescent compound has a longer wavelength than the light emitted by the first phosphorescent compound,
wherein a band having a peak on the longest wavelength side of a function ε(λ)λ ⁴ of the second phosphorescent compound overlaps with a band having a peak of the phosphorescence spectrum F(λ) of the first phosphorescent compound;
where λ denotes a wavelength, and
where ε(λ) denotes a molar absorption coefficient at wavelength λ.

Description

Technical area

The present invention relates to a light-emitting element, a display device, a light-emitting device, an electronic device and a lighting device each using an organic compound as a light-emitting substance.

State of the art

In recent years, intensive research and development has been carried out on light-emitting elements that use electroluminescence (EL). In the basic structure of such a light-emitting element, a layer containing a light-emitting substance (an EL layer) is disposed between a pair of electrodes. By applying voltage to this element, light emission can be obtained from the light-emitting substance.

Such light-emitting elements are self-illuminating elements and have advantages over liquid crystal displays in that they have high pixel visibility and avoid the need for backlighting, so such light-emitting elements are believed to be suitable for flat panel displays. Displays containing such light-emitting elements are also particularly advantageous because they can be thin and light. Another feature of these elements is a high response time.

Since light-emitting layers of these light-emitting elements can be manufactured in the form of a film, it is possible to provide planar light emission. Therefore, large area elements can be easily manufactured. This feature is difficult to achieve with point light sources, typified by incandescent lamps and LEDs, or with linear light sources, typified by fluorescent lamps. Therefore, light-emitting elements have great potential as planar light sources suitable for lighting and the like.

In the case of an organic EL element in which an organic compound is used as a light-emitting substance and the EL layer is provided between a pair of electrodes, applying a voltage between a pair of electrodes causes injection of electrons from a cathode and holes an anode in the EL layer having a light-emitting property and therefore a current flows. By recombining the injected electrons and holes, the organic compound with a light-emitting property is converted into an excited state to provide light emission.

It should be noted that the excited state formed by an organic compound includes a singlet excited state and a triplet excited state, and the luminescence of the singlet excited state (S*) is called fluorescence, whereas the luminescence of the triplet excited state (T *) is called phosphorescence. In addition, the statistical generation ratio of these in the light emitting element is expected to be: S*:T* = 1:3.

In a compound that emits light from the singlet excited state (hereinafter referred to as a fluorescent compound) at room temperature, light emission from the triplet excited state (phosphorescence) is generally not observed, but only light emission from the singlet excited state (fluorescence) is observed becomes. Therefore, the internal quantum efficiency (the ratio of photons generated to carriers injected) of a light-emitting element employing a fluorescent compound is believed to have a theoretical limit of 25% based on the ratio of S* to T*, which is 1:3.

In contrast, for a compound that emits light from the triplet excited state (hereinafter referred to as a phosphorescent compound), light emission from the triplet excited state (phosphorescence) is observed. Furthermore, since intersystem crossing (i.e., the transition from a singlet excited state to a triplet excited state) easily occurs in a phosphorescent compound, the internal quantum efficiency can be increased to 100% in theory. That is, higher emission efficiency can be achieved than when using a fluorescent compound becomes. For this reason, light-emitting elements using phosphorescent compounds are now being actively developed to obtain highly efficient light-emitting elements.

A white light emitting element, which is in the JP 2004 - 522 276 A disclosed includes a light emitting region containing a plurality of types of light emitting dopants that emit phosphorescence.

Light-emitting elements are made from the DE 11 2013 001 468 T5 , the US 2008 / 0 160 345 A1 and the JP 2004- 522 276 A known.

Disclosure of the invention

Although an internal quantum efficiency of 100% is theoretically possible in a phosphorescent compound, such high efficiency can hardly be achieved without optimizing an element structure or a combination with another material. In particular, in a light-emitting element including a variety of types of phosphorescent compounds with different bands (different color emissions) such as light-emitting dopants, it is difficult to obtain high-efficiency light emission without considering not only energy transfer but also efficiency to optimize energy transfer. In fact, in the JP 2004 - 522 276 A Even if all light-emitting dopants of a light-emitting element are phosphorescent compounds, the external quantum efficiency is about 3% to 4%. It is considered that even if the light extraction efficiency is taken into account, the internal quantum efficiency is 20% or less, which is too low for a phosphorescent light-emitting element.

In a multicolor light-emitting element using dopants showing different emission colors, in addition to improving the emission efficiency, it is also necessary to achieve a good balance between the light emissions by the dopants showing different emission colors. It is not easy to maintain a balance between the light emissions of the dopants while achieving high emission efficiency.

In view of the above, an object of an embodiment of the present invention is to provide a light-emitting element which uses a variety of types of light-emitting dopants and has a high emission efficiency. Another object of an embodiment of the present invention is to provide a light emitting device, a display device, an electronic device and a lighting device each having reduced power consumption by using the above light emitting element.

It is only necessary that at least one of the above objects be achieved in the present invention.

In one embodiment of the present invention, the focus is on the Förster mechanism, which is a mechanism of intermolecular energy transfer, and effective energy transfer through the Förster mechanism is achieved by employing a combination of molecules that allow an overlap between an emission spectrum of molecules providing energy and the peak of the longest wavelength side of a characteristic curve obtained by multiplying an absorption spectrum of the molecule receiving energy by a wavelength raised to the fourth energy. Here, one of the characteristics of the above energy transfer is that the energy transfer is not a general energy transfer from a host to a dopant, but an energy transfer from a dopant to a dopant. The light-emitting element of an embodiment of the present invention can be obtained by using such a combination of dopants between which energy can be effectively transferred and forming an element structure so that dopant molecules are suitably isolated.

That is, an embodiment of the present invention is a light-emitting element comprising: a first electrode, a first light-emitting layer, a second light-emitting layer, and a second electrode, the first light-emitting layer disposed between the first electrode and the second light-emitting layer is, wherein the second light-emitting layer is arranged between the first light-emitting layer and the second electrode, the first light-emitting layer comprising: a first phosphorescent compound, a first host material, and a first organic compound, the second light-emitting layer comprising: a second phosphorescent compound dung, and a second host material, wherein the first host material and the first organic compound are capable of forming an exciplex, wherein the light emitted from the second phosphorescent compound has a longer wavelength than the light emitted from the first phosphorescent compound, wherein a band a peak of a function ε(λ)λ4 of the second phosphorescent compound on the longest wavelength side overlaps with a band having a peak of a phosphorescence spectrum F(λ) of the first phosphorescent compound; where λ denotes a wavelength, and where ε(λ) denotes a molar absorption coefficient at wavelength λ.

Further embodiments of the light emitting element of the present invention are described in the subclaims.

Another embodiment of the present disclosure is a light emitting element comprising, between a pair of electrodes, a first light emitting layer in which a first phosphorescent compound is dispersed in a first host material; and a second light-emitting layer in which a second phosphorescent compound is dispersed in a second host material, the second phosphorescent compound emitting light having a longer wavelength than the light emitted by the first phosphorescent compound. A band having a peak of a phosphorescence spectrum of the first phosphorescent compound overlaps with a band having a peak on the longest wavelength side of a function ε(λ)λ ⁴ of the second phosphorescent compound. It should be noted that ε(λ) represents a molar absorption coefficient of each of the phosphorescent compounds and is a function of a wavelength λ.

Another embodiment of the present disclosure is a light-emitting element having the above structure, wherein the first light-emitting layer further contains a first organic compound, the first host material and the first organic compound form an exciplex, and light emitted from the first phosphorescent compound has a longer wavelength than the light emitted by the exciplex.

Still another embodiment of the present disclosure is a light-emitting element having the above structure in which an emission spectrum of the exciplex overlaps with a wavelength of the peak on the longest wavelength side of a function ε(λ)λ ⁴ of the first phosphorescent compound. It should be noted that ε(λ) represents a molar absorption coefficient of each of the phosphorescent compounds and is a function of wavelength λ.

Still another embodiment of the present disclosure is a light-emitting element having the above structure, wherein a band having the peak of the emission spectrum of the exciplex has a band having the peak on the longest wavelength side of the function ε(λ)λ ⁴ of the first phosphorescent compound overlapped. It should be noted that ε(λ) indicates a molar absorption coefficient of each of the phosphorescent compounds and is a function of a wavelength λ.

Still another embodiment of the present disclosure is a light-emitting element having the above structure, wherein the first phosphorescent compound has a phosphorescence peak in a range of 500 nm to 600 nm and the second phosphorescent compound has a phosphorescence peak in a range of 600 nm to 700 nm .

Still another embodiment of the present disclosure is a light-emitting element having the above structure, wherein a recombination region of an electron and a hole is present in the first light-emitting layer.

Still another embodiment of the present disclosure is a light-emitting element having the above structure, wherein the first light-emitting layer is disposed closer to the anode than the second light-emitting layer, and at least in the second light-emitting layer, an electron transport property is higher than a hole transport property.

Still another embodiment of the present disclosure is a light-emitting element having the above structure, wherein the first light-emitting layer is disposed closer to the anode than the second light-emitting layer, and both the first host material and the second host material have an electron transport property. It should be noted that a material having an electron transport property is preferably a material in which an electron transport property is higher than a hole transport property.

Still another embodiment of the present disclosure is a light-emitting element having the above structure, wherein the first light-emitting layer is disposed closer to a cathode than the second light-emitting layer, and at least in the second light-emitting layer, a hole transport property is higher than an electron transport property.

Still another embodiment of the present disclosure is a light emitting element having the above structure, wherein the first light emitting layer is disposed closer to the cathode than the second light emitting layer, and both the first host material and the second host material have a hole transport property. It should be noted that a material having a hole transport property is preferably a material in which a hole transport property is higher than an electron transport property.

Still another embodiment of the present disclosure is a light emitting element having the above structure, wherein the first light emitting layer and the second light emitting layer are stacked in contact with each other.

Still another embodiment of the present invention is a light emitting device, a light emitting display device, an electronic device and a lighting device each including a light emitting element having the above structure.

It should be noted that the light emitting device of this specification includes in the category of an image display device using a light emitting element. Further, the light-emitting device category of this specification includes a module in which a light-emitting element is provided with a terminal such as an anisotropic conductive film or a TCP (tape carrier package); a module in which the top of the TCP is provided with a circuit board; and a module in which an IC (integrated circuit) is directly mounted on a light-emitting element by a COG (chip-on-glass) method. Furthermore, the category includes light-emitting devices used as lighting devices or the like.

An embodiment of the present invention provides a light emitting element with high emission efficiency. By using the light-emitting element, another embodiment of the present invention provides a light-emitting device, a light-emitting display device, an electronic device, and a lighting device, each of which has reduced power consumption.

Brief description of the drawings

• 1A until 1C show conceptual diagrams of light-emitting elements.
• 2A and 2 B show the energy transfer in light-emitting layers.
• 3A and 3B explain the Förster energy transfer.
• 4A and 4B show conceptual diagrams of an active matrix light emitting device.
• 5A and 5B show conceptual diagrams of a passive matrix light-emitting device.
• 6A and 6B show conceptual diagrams of structures of an active matrix light emitting device.
• 7 shows a conceptual diagram of an active matrix type light emitting device.
• 8A and 8B show conceptual diagrams of a lighting device.
• 9A , 9B1 , 9B2 , 9C and 9D show electronic device.
• 10 shows an electronic device.
• 11 shows a lighting device.
• 12 shows a lighting device and a display device.
• 13 shows display devices which are mounted in the motor vehicle and lighting device.
• 14A until 14C show an electronic device.
• 15 shows the luminance-current efficiency characteristics of a light-emitting element 1.
• 16 shows the voltage-luminance properties of a light-emitting element 1.
• 17 shows the luminance-external quantum efficiency properties of a light-emitting element 1.
• 18 shows the luminance-power efficiency properties of a light-emitting element 1.
• 19 shows an emission spectrum of a light-emitting element 1.
• 20A and 20B explain the Förster energy transfer in a light-emitting element 1.
• 21A and 21B explain the Förster energy transfer in a light-emitting element 1.
• 22 explains the Förster energy transfer in a light-emitting element 1.
• 23 shows PL spectra of 2mDBTPDBq-II, PCBA1BP and a mixed foil or film of these.
• 24 shows the luminance-current efficiency properties of a light-emitting element 2.
• 25 shows the voltage-luminance properties of a light-emitting element 2.
• 26 shows the luminance-external quantum efficiency properties of a light-emitting element 2.
• 27 shows the luminance-power efficiency characteristics of a light-emitting element 2.
• 28 shows an emission spectrum of a light-emitting element 2.
• 29 shows a result of a reliability test of a light-emitting element 2.
• 30 shows the luminance-current efficiency properties of a light-emitting element 3.
• 31 shows the voltage-luminance properties of a light-emitting element 3.
• 32 shows the luminance-external quantum efficiency properties of a light-emitting element 3.
• 33 shows the luminance-power efficiency characteristics of a light-emitting element 3.
• 34 shows an emission spectrum of a light-emitting element 3.
• 35 shows the luminance-current efficiency properties of a light-emitting element 4.
• 36 shows the voltage-luminance properties of a light-emitting element 4.
• 37 shows the luminance-external quantum efficiency properties of a light-emitting element 4.
• 38 shows the luminance-power efficiency characteristics of a light-emitting element 4.
• 39 shows an emission spectrum of a light-emitting element 4.
• 40 shows the luminance-current efficiency properties of a light-emitting element 5.
• 41 shows the voltage-luminance properties of a light-emitting element 5.
• 42 shows the luminance-external quantum efficiency properties of a light-emitting element 5.
• 43 shows the luminance-power efficiency characteristics of a light-emitting element 5.
• 44 shows an emission spectrum of a light-emitting element 5.
• 45A and 45B explain the Förster energy transfer in a light-emitting element 4.
• 46 explains the Förster energy transfer in a light-emitting element 4.
• 47A and 47B explain the Förster energy transfer in a light-emitting element 5.
• 48A and 48B explain the Förster energy transfer in a light-emitting element 5.
• 49 explains the Förster energy transfer in a light-emitting element 5.

Best way to carry out the invention

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. It should be noted that the present invention is not limited to the description set forth below, and it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention. Therefore, the present invention should not be construed as being limited to the description of the embodiments set forth below.

Embodiment 1

First, an operating principle of a light emitting element of an embodiment of the present invention will be described. The point of the present invention is that a first phosphorescent compound and a second phosphorescent compound which emits light having a longer wavelength than the light emitted from the first phosphorescent compound are used, and both the first and second phosphorescent compounds emit light emit efficiently, thereby obtaining a multicolor light-emitting element with high efficiency.

As a general method, in order to obtain a multicolor light-emitting element containing a phosphorescent compound, there can be given a method in which a plurality of types of phosphorescent compounds having different emission colors are dispersed in a host material at an appropriate ratio. In such a method, the phosphorescent compound which emits light with the longest wavelength easily emits light, so it is extremely difficult to design and control a structure (particularly the concentration of the phosphorescent compounds in the host material) to produce polychromatic light receive.

As another method for obtaining a multicolor light-emitting element, a tandem structure in which light-emitting elements having different emission colors are stacked on each other can be cited. For example, a blue light-emitting element, a green light-emitting element, and a red light-emitting element are stacked in this order and emit light at the same time, whereby polychromatic light (in this case, white light) can be easily obtained. The element structure can be constructed and controlled relatively easily because the blue light-emitting element, the green light-emitting element and the red light-emitting element can be optimized independently. However, stacking the three elements is accompanied by an increase in the number of layers and makes manufacturing complicated. Furthermore, if there is a problem in electrical contact at the connection areas between the elements (called interlayers), an increase in the driving voltage may occur, i.e. H. a loss of power can be caused.

In contrast, in the light-emitting element of an embodiment of the present invention, between the pair of electrodes, the first light-emitting layer in which the first phosphorescent compound is dispersed in the first host material and the second light-emitting layer in which the second phosphorescent compound which emits light is stacked emitted with a longer wavelength than the light emitted by the first phosphorescent compound, is dispersed in the second host material. In contrast to the case of a tandem structure, the first and second light-emitting layers may be provided in contact with each other.

An element structure of the above-described light-emitting element of an embodiment of the present invention is shown in Figs 1A until 1C shown schematically. In 1C a first electrode 101, a second electrode 102 and an EL layer 103 are shown. The EL layer 103 includes at least one light emitting layer 113, and other layers may be provided as appropriate. In the in 1C The structure shown assumes that a hole injection layer 111, a hole transport layer 112, an electron transport layer 114 and an electron injection layer 115 are provided. It should be noted that it is assumed that the first electrode 101 serves as an anode and the second electrode 102 serves as a cathode.

The 1A and 1B are enlarged views of the light emitting layer 113 of the light emitting element. In each of the 1A and 1B are a first light-emitting layer 113a, a second light-emitting layer 113b, the light-emitting layer 113 which is a combination of the two layers, a first phosphorescent compound 113Da, a second phosphorescent compound dung 113Db, a first host material 113Ha and a second host material 113Hb. 1B Fig. 12 shows a schematic diagram illustrating the case where the first light-emitting layer 113a further contains a first organic compound 113A. In any case, the phosphorescent compounds (the first and second phosphorescent compounds) are dispersed in the host materials so that the phosphorescent compounds are isolated from each other by the host materials. It should be noted that the first and second host materials may be the same or different from each other. The first light-emitting layer 113a may be disposed on the anode side and the second light-emitting layer 113b may be disposed on the cathode side, or the first light-emitting layer 113a may be disposed on the cathode side and the second light-emitting layer 113b may be disposed on the anode side.

In this case, energy transfer between the phosphorescent compounds is suppressed through electron exchange interaction (which is called the Dexter mechanism). In other words, a phenomenon in which, after the first phosphorescent compound 113Da is excited, the excitation energy is transferred to the second phosphorescent compound 113Db through the Dexter mechanism can be prevented. Therefore, a phenomenon in which the second phosphorescent compound 113Db, which emits light with the longest wavelength, mainly emits light, can be suppressed. It should be noted that the second phosphorescent compound 113Db emits light mainly in the case where an exciton is directly generated in the second light-emitting layer 113b; therefore, it is preferable that a recombination region of the carriers is present in the first light-emitting layer 113a (i.e., mainly the first phosphorescent compound 113Da is excited).

It should be noted that when the energy transfer of the first phosphorescent compound 113Da is completely suppressed, light emission from the second phosphorescent compound 113Db cannot be obtained. Therefore, in an embodiment of the present invention, the element design is such that the excitation energy of the first phosphorescent compound 113Da is partially transferred to the second phosphorescent compound 113Db. Such energy transfer between isolated molecules is possible by using the dipole-dipole interaction (Förster mechanism).

The Förster mechanism is described below. The molecules that release excitation energy and the molecules that absorb excitation energy are referred to below as energy donors and energy acceptors. That is, in one embodiment of the present invention, both the energy donor and the energy acceptor are phosphorescent compounds and are isolated from each other by the host materials.

In the Förster mechanism, direct intermolecular contact is not necessary for energy transfer. Energy transfer occurs through a resonance phenomenon of dipolar oscillation between an energy donor and an energy acceptor. The resonance phenomenon of dipolar oscillation causes the energy donor to release energy to the energy acceptor; therefore, the energy donor in an excited state relaxes to a ground state and the energy acceptor in a ground state is excited. The rate constant k _F of energy transfer through the Förster mechanism is expressed by a formula (1).
formula 1 $$k_F=\frac{9000c^4{\mathrm{<figure-callout\; id="2"\; label="K"\; filenames="DE112013007781B4\_0027.png,DE112013007781B4\_0039.png"\; state="\{\{state\}\}">K</figure-callout>}}^2\varphi \text{ln10}}{128{\pi }^5{n}^{4}N\tau {\mathrm{<figure-callout\; id="6"\; label="R"\; filenames="DE112013007781B4\_0039.png"\; state="\{\{state\}\}">R</figure-callout>}}^6}{\displaystyle \int \frac{F\left(v\right)\epsilon \left(v\right)}{v^4}}dv$$

In the formula (1), v indicates a frequency, F(v) indicates a normalized emission spectrum of an energy donor (a fluorescence spectrum in energy transfer from a singlet excited state and a phosphorescence spectrum in energy transfer from a triplet excited state), ε(v) indicates a molar absorption coefficient of an energy acceptor, N indicates Avogadro's number, n indicates a refractive index of a medium, R indicates an intermolecular distance between the energy donor and the energy acceptor, r indicates a measured lifetime of an excited state (fluorescence lifetime or phosphorescence lifetime), c indicates the speed of light, ϕ indicates a luminescence quantum yield (a fluorescence quantum yield in energy transfer from a singlet excited state and a phosphorescence quantum yield in energy transfer from a triplet excited state), and K ² indicates a coefficient (0 to 4) of the orientation tion of a transition dipole moment between the energy donor and the energy acceptor. It should be noted that K ² = 2/3 in statistical orientation.

As formula (1) suggests, the following can be given as necessary conditions for energy transfer through the Förster mechanism (Förster energy transfer): 1. the energy donor and the energy acceptor are not too far apart (as far as the distance R is concerned) ; 2 the energy donor emits light (as far as the luminescence quantum yield ϕ is concerned); and 3. an emission spectrum of the energy donor overlaps with an absorption spectrum of the energy acceptor (as far as the integral part is concerned).

As already with regard to the 1A until 1C described, the phosphorescent compounds (the first and second phosphorescent compounds) are dispersed in the respective host materials and isolated from each other by the host materials; therefore, the distance R is at least one molecule length or more (ie, 1 nm or more). Therefore, the excitation energy generated in the first phosphorescent compound is not fully transferred to the second phosphorescent compound through the Förster mechanism. Förster energy transfer at the distance R can occur when R is less than about 10 nm to 20 nm or equal to 10 nm to 20 nm. So that the distance R of at least one molecule length or more between the first and second phosphorescent compounds is ensured, the mass of the phosphorescent compound dispersed in the host material is preferably set to a certain mass or less than this. Based on this, the concentration of the phosphorescent compound in the light-emitting layer is 10% by weight or less. If the concentration of the phosphorescent compound is too low, it is difficult to obtain preferable properties; therefore, the concentration of the phosphorescent compound in this embodiment is preferably 0.1 wt% or more and 10 wt% or less. In particular, it is preferable that the first phosphorescent compound is contained in the first light-emitting layer 113a at a concentration of 0.1 wt% or more and 5 wt% or less.

The 2A and 2 B schematically illustrate the Förster energy transfer between the phosphorescent compounds in the light emitting layer of an embodiment of the present invention, wherein the first phosphorescent compound 113Da and the second phosphorescent compound 113Db emitting light with a longer wavelength than the light emitted by the first phosphorescent compound , are included. In each of the 2A and 2 B 1, a structure in which the first light-emitting layer 113a and a second light-emitting layer 113b are stacked between an electrode 10 and an electrode 11 is shown. It should be noted that one of the electrode 10 and the electrode 11 serves as an anode and the other as a cathode. As in 2A shown, an excited singlet state, which is formed in the first phosphorescent compound 113Da (S _a ), is first converted into a triplet excited state (T _a ) by intersystem crossing. In other words, an exciton in the first light-emitting layer 113a is brought substantially to T _a .

Subsequently, the energy of the exciton in the T _a state, some of which is converted into light emission, can be partially transferred to the triplet excited state of the second phosphorescent compound 113Db (T _b ) through the Förster mechanism. This results from the fact that the first phosphorescent compound 113Da has a light-emitting property (possesses a high phosphorescence quantum yield ϕ) and that direct absorption, which corresponds to an electron transition from a singlet ground state to a triplet excited state, is observed in the second phosphorescent compound 113Db ( an absorption spectrum of an excited triplet state exists). If these conditions are met, a triplet-triplet Förster energy transfer from T _a to T _b is possible.

It should be noted that in many cases a singlet excited state of the second phosphorescent compound 113Db (S _b ) has a higher energy than the triplet excited state of the first phosphorescent compound 113Da (T _a ) and therefore in many cases does not contribute as much to the above energy transfer contributes. For this reason the description is omitted here. Needless to say, when the singlet excited state of the second phosphorescent compound 113Db (S _b ) has a lower energy than the triplet excited state of the first phosphorescent compound 113Da (T _a ), energy transfer may occur similarly. In this case, the transferred to the excited singlet state of the second phosphorescent compound 113Db (S _b ). Energy transferred to the triplet excited state of the second phosphorescent compound 113Db (T _b ) through intersystem crossing to contribute to light emission.

It should be noted that in order for the above Förster energy transfer to occur efficiently between the phosphorescent compounds serving as dopants and not to the host materials, it is preferred that the absorption spectra of the first and second host materials not be in the emission region of the first phosphorescent Connection 113Lying there. In this way, when energy is directly transferred between dopants without being transferred through the host material (particularly the second host material), the formation of an extra path of energy transfer can be suppressed and high emission efficiency can be achieved, which is preferable.

Furthermore, the first host material preferably has a triplet excitation energy which is higher than that of the first phosphorescent compound in order not to quench the first phosphorescent compound.

As described above, a basic concept of an embodiment of the present invention is an element structure in which the first phosphorescent compound which emits light with a shorter wavelength is mainly excited in a state in which the first and second phosphorescent compounds are separated from each other using the host materials and the stacked layer structure are isolated. Since the energy is partially transferred by the Förster mechanism over a certain distance (20 nm or less) in such an element structure, the excitation energy of the first phosphorescent compound is partially transferred to the second phosphorescent compound. As a result, light emission from each of the first and second phosphorescent compounds can be obtained.

More importantly, in an embodiment of the present invention, the materials and element structure are selected taking into account the above energy transfer.

For Förster energy transfer to occur, the energy donor must have a high luminescence quantum yield ϕ. Regarding the luminescence quantum yield, there is no problem in an embodiment of the present invention because a phosphorescent compound (particularly a light-emitting compound having a phosphorescence quantum yield of 0.1 or more) is used. An important point is that the integral part of formula (1) is large, i.e. that is, an emission spectrum F(v) of the energy donor appropriately overlaps with the molar absorption coefficient ε(v) of the energy acceptor.

In general, it is assumed that the emission spectrum F(v) of the energy donor must simply overlap with a wavelength range in which the molar absorption coefficient ε(v) of the energy acceptor is large (i.e., the product of F(v) and ε(v) just has to be big). However, this is not necessarily true for the Förster mechanism since the integral component in formula (1) is inversely proportional to the frequency v, which is raised to the fourth power to have a wavelength dependence.

For easier understanding, formula (1) is transformed here. Since v = c/λ, where λ indicates a wavelength of light, formula (1) can be transferred into a formula (2).

In other words, it becomes clear that the longer the wavelength λ, the larger the integral component becomes. In simpler terms, it is suggested that energy transfer occurs more easily on the longer wavelength side. That is, it is not so simple that F(λ) must overlap with the wavelength range in which the molar absorption coefficient ε(λ) is large. It is necessary that F(λ) overlaps with a region in which ε(λ)λ ⁴ is large.

Therefore, in the light-emitting element of an embodiment of the present invention, in order to increase the efficiency of energy transfer from the first phosphorescent compound 113Da, a phosphorescent compound which enables a band having a maximum value of an emission spectrum of the first phosphorescent compound 113Da to be formed with a band with the peak on the longest wavelength side of the function ε(λ)λ ⁴ of the second phosphorescent compound 113Db is used as the second phosphorescent compound 113Db.

It should be noted that the wavelength of the peak on the longest wavelength side of the function ε(λ)λ ⁴ of the second phosphorescent compound is preferably with a phosphor rescence spectrum F(λ) of the first phosphorescent compound overlaps. Further, it is more preferable that a wavelength range in which the band having the above maximum value of the emission spectrum of the first phosphorescent compound 113Da has half the intensity of the above maximum value overlaps with a wavelength range in which the band having the above peak Function ε(λ)λ ⁴ of the second phosphorescent compound has half the intensity of the above peak, in which case the overlap between the spectra can be greater.

In a light-emitting element having the structure described above, high emission efficiency can be achieved, and the phosphorescent compound can provide light emissions in a good balance.

For a better understanding of such structures of the phosphorescent compound, an explanation will be given below with reference to specific examples. Here, as an example, a case will be described in which a compound (1) shown below (bis[2-(6-tert-butyl-4-pyrimidinyl-κN3)phenyl-κC](2,4-pentanedionato- κ ² O,O')iridium(III) (abbreviation: Ir(tBuppm) ₂ (acac))) is used as the first phosphorescent compound 113Da and a compound (2) shown below (Bis(2,3, 5-triphenylpyrazinato)(dipivaloylmethanato)iridium(III) (abbreviation: Ir(tppr) ₂ (dpm))) is used as the second phosphorescent compound 113Db, which emits light with a longer wavelength than that emitted by the first phosphorescent compound 113Da Light.

3A shows a molar absorption coefficient ε(λ) and ε(λ)λ ⁴ of the compound (2), which is the second phosphorescent compound. The molar absorption coefficient ε(λ) becomes smaller on a longer wavelength side, but ε(λ)λ ⁴ has the peak at about 550 nm (corresponding to a triplet MLCT absorption band of the compound (2)). From this example, it is clear that influenced by the expression λ ⁴ , ε(λ)λ ⁴ of the second phosphorescent compound has the peak in the absorption band (triplet MLCT absorption band) located on the longest wavelength side.

3B shows a photoluminescence (PL) spectrum F(λ) of the compound (1) and ε(λ)λ ⁴ of the compound (2). Compound (1) is the first phosphorescent compound and emits green light with an emission peak at approximately 545 nm. Around the peak on the longest wavelength side of ε(λ)λ ⁴ of the second phosphorescent compound overlaps the PL spectrum F(λ ) of the first phosphorescent compound largely with ε(λ)λ ⁴ and the energy transfer from the first phosphorescent compound to the second phosphorescent compound occurs through the Förster mechanism. It should be noted that in this case that the peak corresponds to the triplet MLCT absorption band, the energy transfer is the triplet-triplet Förster energy transfer (T _a -T _b energy transfer in the 2A and 2 B) . At this time, the difference between the emission peak wavelength of the PL spectrum F(λ) of the first phosphorescent compound and the wavelength of the peak on the longest wavelength side of ε(λ)λ ⁴ of the second phosphorescent compound is preferably 0.2 eV or less , in which case the energy transfer occurs efficiently. The emission peak wavelength of the PL spectrum F(λ) of the compound (1) is 546 nm and the wavelength of the peak on the longest wavelength side of ε(λ)λ ⁴ of the compound (2) is 543 nm, the difference being 3 nm is, corresponding to 0.01 eV. It can therefore be seen that the energy transfer between connection (1) and connection (2) occurs very efficiently.

It should be noted that according to the above, it is preferable that the absorption spectrum of the second phosphorescent compound on the longest wavelength side shows direct absorption corresponding to an electron transition from a singlet ground state to a triplet excited state (e.g., triplet MLCT absorption ). Such a structure leads to a high efficiency of the triplet-triplet energy transfer, which occurs in the 2A and 2 B is shown.

In order to obtain the above-described recombination region, in the case where the first light-emitting layer 113a is disposed on the anode side, at least the second light-emitting layer 113b may preferably have an electron transport property and both the first light-emitting layer 113a and the second light-emitting layer Layer 113b may have an electron transport property. In the case where the first light emitting layer 113a is disposed on the cathode side, at least the second light emitting layer 113b preferably has a hole transport property, and both the first light emitting layer 113a and the second light emitting layer 113b may have a hole transport property.

In addition, in the first light-emitting layer 113a, it is preferable that a band having a peak of the photoluminescence (PL) spectrum F(λ) of the first host material 113Ha clearly coincides with a band having the peak on the longest wavelength side of the function ε(λ )λ ⁴ of the first phosphorescent compound overlaps.

In general, however, it is difficult to find an overlap between a band having a peak of a photoluminescence (PL) spectrum F(λ) of a host material and a band having the peak on the longest wavelength side of the function ε(λ)λ ⁴ of a guest material (first phosphorescent compound 113Da). The reason for this is that the photoluminescence (PL) of the host material is generally fluorescence, that is, light emission of a higher energy level than that of phosphorescence, so there is a high probability of a triplet excitation energy level of the host material, whose fluorescence spectrum is at a wavelength in near an absorption spectrum on the longest wavelength side of the guest material (a triplet excited state of a guest material) becomes lower than a triplet excitation energy level of the guest material. When the triplet excitation energy level of the host material becomes lower than the triplet excitation energy level of the guest material, the triplet excitation energy of the guest material is transferred to the host material, resulting in a reduction in emission efficiency.

Therefore, in this embodiment, it is preferable that the first light-emitting layer 113a further contains the first organic compound 113A, and the first host material 113Ha and the first organic compound 113A form an exciplex (also called an excited complex) 113Ec ( 1B and 2 B) . In the 2 B 10 and 11 denote electrodes, one of which serves as an anode and the other serves as a cathode. It should be noted that in the drawings, a singlet excited state and a triplet excited state of the exciplex 113Ec are represented by S _e and T _e , as a singlet excited state and a triplet excited state of the first phosphorescent compound 113Da are represented by S _a and T _{a and a} Singlet excited state and triplet excited state of the second phosphorescent compound 113Db are represented by S _b and T _b .

In that case, at the time of recombination, the carriers (electrons and holes) in the first light-emitting layer 113a, the first organic compound 113A and the first host material 113Ha form the exciplex 113Ec by absorbing energy as a result of the recombination of the electrons and holes. Fluorescence from the exciplex 113Ec has a spectrum on a longer wavelength side with respect to a fluorescence spectrum of the first organic compound 113A alone and a fluorescence spectrum of the first host material 113Ha alone, and also has a property that the singlet excited state S _e and the triplet excited state T _e of the Exciplex 113Ec are extremely close to each other in terms of energy. Therefore, when a band having a peak of a PL spectrum F(λ) showing light emission from the excited singlet state of the Exciplex 113Ec is matched with the band having the peak on the longest wavelength side of the function ε(λ)λ ⁴ of the guest material ( the first phosphorescent compound 113Da) (which corresponds to an absorption spectrum of an excited triplet state T _a of the guest material), both the energy transfer from S _e to T _a and the energy transfer from T _e to T _a can be increased as much as possible. In this

In this case, a difference between an emission peak wavelength of the exciplex 113Ec and a wavelength of a peak of ε(λ)λ ⁴ of the guest material (the first phosphorescent compound 113Da) is preferably 0.2 eV or less, in which case energy transfer occurs efficiently. The vastness ren, the triplet excitation energy levels of the first organic compound 113A and the first host material 113Ha are preferably kept higher than the triplet excitation energy level of the first phosphorescent compound 113Da.

A part of the energy thus transferred to the first phosphorescent compound 113Da is transferred to the second phosphorescent compound 113Db as described above, so that both the first phosphorescent compound 113Da and the second phosphorescent compound 113Db efficiently emit light.

It should be noted that the energy transfer from the triplet excited state (T _e ) of the exciplex 113Ec to the first phosphorescent compound 113Da occurs efficiently through the Dexter mechanism. Energy transfer from the excited singlet state (S _e ) occurs efficiently through the Förster mechanism described above, thereby achieving sufficient energy transfer as a whole.

There is no particular limitation on the first organic compound 113A and the first host material 113Ha as long as they can form an exciplex; a combination of a compound which tends to accept electrons (a compound having an electron-capturing property) and a compound which tends to accept holes (a compound having a hole-capturing property) is preferably used.

The following are examples of the compound which tends to accept electrons: a metal complex such as bis(10-hydroxybenzo[h]quinolinato)beryllium(II) (abbreviation: BeBq ₂ ), bis(2-methyl-8-quinolinolato)(4 -phenylphenolato)aluminium(III) (abbreviation: BAlq), bis(8-quinolinolato)zinc(II) (abbreviation: Znq), bis[2-(2-benzoxazolyl)phenolato]zinc(lI) (abbreviation: ZnPBO) or Bis[2-(2-benzothiazolyl)phenolato]zinc(II) (abbreviation: ZnBTZ); a heterocyclic compound with a polyazole skeleton, such as 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation: PBD), 3-(4-biphenylyl)-4-phenyl -5-(4-tert-butylphenyl)-1,2,4-triazole (abbreviation: TAZ), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazole-2- yl]benzene (abbreviation: OXD-7), 9-[4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl]-9H-carbazole (abbreviation: CO11), 2,2', 2"-(1,3,5-benzenetriyl)tris(1-phenyl-1H-benzimidazole) (abbreviation: TPBI) or 2-[3-(dibenzothiophen-4-yl)phenyl]-1-phenyl-1H-benzimidazole (Abbreviation: mDBTBIm-II); a heterocyclic compound with a diazine skeleton, such as 2-[3-(Dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (Abbreviation: 2mDBTPDBq-II), 2-[3' -(Dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTBPDBq-II), 2-[3'-(9H-carbazol-9-yl)biphenyl-3-yl] dibenzo[fh]quinoxaline (abbreviation: 2mCzBPDBq), 4,6-bis[3-(phenanthren-9-yl)phenyl]pyrimidine (abbreviation: 4.6mPnP2Pm) or 4,6-bis[3-(4-dibenzothienyl) phenyl]pyrimidine (abbreviation: 4.6mDBTP2Pm-II); and a heterocyclic compound having a pyridine skeleton have high reliability and are therefore preferred. In particular, a heterocyclic compound having a diazine (pyrimidine or pyrazine) skeleton has a high electron transport property to contribute to reducing the driving voltage.

The following are examples of the compound which tends to accept holes: a compound having an aromatic amine skeleton, such as 4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB), N, N'-Bis(3-methylphenyl)-N,N'-diphenyl-[1,1'-biphenyl]-4,4'-diamine (abbreviation: TPD), 4,4'-Bis[N-(spiro- 9,9'-bifluoren-2-yl)-N-phenylamino]biphenyl (abbreviation: BSPB), 4-phenyl-4'-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP), 4-phenyl- 3'-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: mBPAFLP), 4-phenyl-4'-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBA1BP), 4,4' -Diphenyl-4"-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBBi1BP), 4-(1-naphthyl)-4'-(9-phenyl-9H-carbazol-3-yl) triphenylamine (abbreviation: PCBANB), 4,4'-Di(1-naphthyl)-4"-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBNBB), 9,9-dimethyl-N- phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]fluoren-2-amine (abbreviation: PCBAF) or N-phenyl-N-[4-(9-phenyl-9H-carbazole -3-yl)phenyl]spiro-9,9'-bifluoren-2-amine (abbreviation: PCBASF); a compound with a carbazole skeleton, such as 1,3-bis(N-carbazolyl)benzene (abbreviation: mCP), 4,4'-di(N-carbazolyl)biphenyl (abbreviation: CBP), 3,6-bis(3, 5-diphenylphenyl)-9-phenylcarbazole (abbreviation: CzTP) or 3,3'-bis(9-phenyl-9H-carbazole) (abbreviation: PCCP); a compound with a thiophene skeleton, such as 4,4',4"-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation: DBT3P-II), 2,8-diphenyl-4-[4-( 9-phenyl-9H-fluoren-9-yl)phenyl]dibenzothiophene (abbreviation: DBTFLP-III) or 4-[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-6-phenyldibenzothiophene (abbreviation: DBTFLP-IV); and a compound with a furan skeleton, such as 4,4',4"-(benzene-1,3,5-triyl)tri(dibenzofuran) (abbreviation: DBF3P-II) or 4-{3-[ 3-(9-Phenyl-9H-fluoren-9-yl)phenyl]phenyl}dibenzofuran (abbreviation: mmDBFFLBi-II). Among the above materials, a compound having an aromatic amine skeleton and a compound having a carbazole skeleton are preferred because these compounds are very reliable and have high hole transport properties to help reduce the driving voltage.

The first organic compound 113A and the first host material 113Ha are not limited to the compounds as long as they can form an exciplex, the band having the peak of the photoluminescence (PL) spectrum F(λ) of the exciplex having the band having the peak at the Side of the longest wavelength of the function ε (λ) λ ⁴ of the first phosphorescent compound overlaps and the peak of an emission spectrum of the exciplex has a longer wavelength than a peak of the emission spectrum of the first phosphorescent compound 113Da.

It should be noted that in the case where a compound that tends to accept electrons and a compound that tends to accept holes are used as the first organic compound 113A and the first host material 113Ha, the carrier balance is carried out the mixing ratio of the compounds can be controlled. In particular, the ratio of the first organic compound 113A to the first host material 113Ha is preferably from 1:9 to 9:1.

In this structure, the first host material 113Ha and the first organic compound 113A are selected to form an exciplex, which allows the band having the peak of the photoluminescence (PL) spectrum F(λ) of the exciplex to coexist with the band overlaps the peak on the longest wavelength side of the function ε(λ)λ ⁴ of the first phosphorescent compound. It is preferred that the overlap between the bands be as large as possible.

It should be noted that a wavelength of the peak on the longest wavelength side of the function ε(λ)λ ⁴ of the first phosphorescent compound preferably overlaps with the photoluminescence (PL) spectrum F(λ) of the exciplex. Furthermore, it is more preferable. that a wavelength range in which the band with the peak of the photoluminescence (PL) spectrum F(λ) of the exciplex has half the intensity of the above peak overlap with a wavelength range in which the band with the peak of the function ε(λ)λ ⁴ of the first phosphorescent compound has half the intensity of the above peak, in which case the overlap between the spectra may be greater.

In the structure, energy can be effectively transferred from the exciplex formed of the first host material 113Ha and the first organic compound 113A to the first phosphorescent compound 113Da to increase the energy transfer efficiency, whereby a light-emitting element with a higher external quantum efficiency can be obtained .

Embodiment 2

In this embodiment, a detailed example of the structure of the light emitting element described in Embodiment 1 will be described below with reference to FIG 1A until 1C described.

A light-emitting element in this embodiment includes an EL layer containing a plurality of layers between a pair of electrodes. In this embodiment, the light emitting element includes the first electrode 101, the second electrode 102, and the EL layer 103 provided between the first electrode 101 and the second electrode 102. It should be noted that in this embodiment, the description is made assuming that the first electrode 101 serves as an anode and that the second electrode 102 serves as a cathode. In other words, when a voltage is applied between the first electrode 101 and the second electrode 102 so that the potential of the first electrode 101 is higher than that of the second electrode 102, light emission can be obtained.

Since the first electrode 101 serves as the anode, the first electrode 101 is preferably formed using metals, alloys, electrically conductive compounds having a high work function (particularly a work function of 4.0 eV or more), mixtures thereof, and the like. Specifically, as an example, indium oxide-tin oxide (ITO: indium tin oxide), indium oxide-tin oxide containing silicon or silicon oxide, indium oxide-zinc oxide, indium oxide containing tungsten oxide and zinc oxide (IWZO) and the like can be given. Films of these electrically conductive metal oxides are generally formed by a sputtering method, but may also be formed by using a sol-gel method or the like. In an example of the manufacturing process, indium oxide-zinc oxide is deposited by a sputtering method using a target obtained by adding 1 wt% to 20 wt% zinc oxide to indium oxide. Further, a film of indium oxide containing tungsten oxide and zinc oxide (IWZO) can be formed by a sputtering method using a target in which tungsten oxide and zinc oxide are formed into indium oxide at 0.5 wt% to 5 wt% and 0.1 % by weight to 1% by weight can also be added. In addition, gold (Au), platinum (Pt), nickel (Ni), tungsten (W), chromium (Cr), molybdenum (Mo), iron (Fe), Cobalt (Co), copper (Cu), palladium (Pd), nitrides of metal materials (e.g. titanium nitride) and the like. Graphene can also be used. It should be noted that when a composite material described later is used as a layer in contact with the first electrode 101 in the EL layer 103, an electrode material can be selected regardless of the work function.

There is no particular limitation on the stacked layer structure of the EL layer 103 as long as the EL layer includes the light emitting layer 113 having a structure similar to that described in Embodiment 1. For example, the EL layer 103 may be formed by combining a hole injection layer, a hole transport layer, the light emitting layer, an electron transport layer, an electron injection layer, a carrier blocking layer, an intermediate layer and the like as appropriate. In this embodiment, the EL layer 103 has a structure in which the hole injection layer 111, the hole transport layer 112, the light emitting layer 113, the electron transport layer 114 and the electron injection layer 115 are stacked on the first electrode 101 in this order. The materials contained in the layers are specifically stated below.

The hole injection layer is a layer containing a substance having a high hole injection property. Molybdenum oxide, vanadium oxide, ruthenium oxide, tungsten oxide, manganese oxide or the like can be used. Alternatively, the hole injection layer 111 may be formed using a phthalocyanine-based compound such as phthalocyanine (abbreviation: H ₂ Pc) or copper phthalocyanine (abbreviation: CuPc), an aromatic amine compound such as 4,4'-bis[N-(4-diphenylaminophenyl)- N-phenylamino]biphenyl (abbreviation: DPAB) or N,N'-Bis{4-[bis(3-methylphenyl)amino]phenyl}-N,N'-diphenyl-(1,1'-biphenyl)-4, 4'-diamine (abbreviation: DNTPD), a high molecular weight compound such as poly(ethylenedioxythiophene)/poly(styrenesulfonic acid) (PEDOT/PSS) or the like.

Alternatively, a composite material may be used for the hole injection layer 111, in which a substance having a hole transport property contains a substance having an acceptor property. It should be noted that the use of such a substance having a hole transport property containing a substance having an acceptor property enables selection of a material used to form an electrode regardless of its work function. In other words, in addition to a material with a high work function, a material with a low work function can also be used as the first electrode 101. As the substance having the acceptor property, there can be mentioned 7,7,8,8-tetra-cyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation: F ₄ -TCNQ), chloranil and the like. Additionally, transition metal oxides can be mentioned. Oxides of metals belonging to Group 4 to Group 8 of the periodic table may be cited. In particular, vanadium oxide, niobium oxide, tantalum oxide, chromium oxide, molybdenum oxide, tungsten oxide, manganese oxide and rhenium oxide are preferred because their electron-accepting property is high. Among them, molybdenum oxide is particularly preferred because it is stable in air, has low hygroscopic property and is easily treated.

As the substance having a hole transport property used for the composite material, any of a variety of organic compounds such as aromatic amine compounds, carbazole derivatives, aromatic hydrocarbons and high molecular weight compounds (e.g. oligomers, dendrimers or polymers) can be used. It should be noted that the organic compound used for the composite material is preferably an organic compound having a high hole transport property. In particular, a substance having a hole mobility of 10 ^-6 cm ² /Vs or more is preferably used. Organic compounds that can be used as the substance having a hole transport property in the composite material are specifically mentioned below.

Examples of the aromatic amine compounds are N,N-Di(p-tolyl)-N,N'-diphenyl-p-phenylenediamine (abbreviation: DTDPPA), 4,4'-Bis[N-(4-diphenylaminophenyl)-N- phenylamino]biphenyl (abbreviation: DPAB), N,N'-Bis{4-[bis(3-methylphenyl)amino]phenyl}-N,N'-diphenyl-(1,1'-biphenyl)-4,4' -diamine (abbreviation: DNTPD), 1,3,5-Tris[N-(4-diphenylaminophenyl)-N-phenylami-no]benzene (abbreviation: DPA3B) and the like.

Specific examples of the carbazole derivatives that can be used for the composite material are 3-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole (abbreviation: PCzPCA1), 3,6-Bis[ N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole (abbreviation: PCzPCA2), 3-[N-(1-naphthyl)-N-(9-phenylcarbazol-3-yl)amino] -9-phenylcarbazole (abbreviation: PCzPCN1) and the like.

Other examples of the carbazole derivatives that can be used for the composite material are 4,4'-di(N-carbazolyl)biphenyl (abbreviation: CBP), 1,3,5-tris[4-(N-carbazolyl)phenyl]benzene (Abbreviation: TCPB), 9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (Abbreviation: CzPA), 1,4-Bis[4-(N-carbazolyl)phenyl]-2, 3,5,6-tetraphenylbenzene and the like.

Examples of the aromatic hydrocarbons that can be used for the composite material are 2-tert-butyl-9,10-di(2-naphthyl)anthracene (abbreviation: t-BuDNA), 2-tert-butyl-9,10- di(1-naphthyl)anthracene, 9,10-bis(3,5-diphenylphenyl)anthracene (abbreviation: DPPA), 2-tert-butyl-9,10-bis(4-phenylphenyl)anthracene (abbreviation: t-BuDBA ), 9,10-di(2-naphthyl)-anthracene (abbreviation: DNA), 9,10-diphenylanthracene (abbreviation: DPAnth), 2-tert-butylanthracene (abbreviation: t-BuAnth), 9,10-Bis( 4-methyl-1-naphthyl)anthracene (abbreviation: DMNA), 2-tert-butyl-9,10-bis[2-(1-naphthyl)phenyl]anthracene, 9,10-bis[2-(1-naphthyl )phenyl)anthracene, 2,3,6,7-tetramethyl-9,10-di(1-naphthyl)anthracene, 2,3,6,7-tetramethyl-9,10-di(2-naphthyl)anthracene, 9,9'-bianthryl, 10,10'-diphenyl-9,9'-bianthryl, 10,10'-bis(2-phenylphenyl)-9,9'-bianthryl, 10,10'-bis[(2, 3,4,5,6-pentaphenyl)phenyl]-9,9'-bianthryl, anthracene, tetracene, rubrene, perylene, 2,5,8,11-tetra(tert-butyl)perylene and the like. In addition, pentacene, coronene or the like can also be used. The aromatic hydrocarbon which has a hole mobility of 1 × 10 ^-6 cm ² /Vs or more and which has 14 to 42 carbon atoms is particularly preferred.

It should be noted that the aromatic hydrocarbons that can be used for the composite material may have a vinyl skeleton. Examples of the aromatic hydrocarbon with a vinyl group are 4,4'-bis(2,2-diphenylvinyl)biphenyl (abbreviation: DPVBi), 9,10-bis[4-(2,2-diphenylvinyl)phenyl]anthracene (abbreviation: DPVPA ) and the same.

A high molecular weight compound such as poly(N-vinylcarbazole) (abbreviation: PVK), poly(4-vinyltri-phenylamine) (abbreviation: PVTPA), poly[N-(4-{N'-[4-(4-diphenylamino)phenyl). ]phenyl-N'-phenyl-amino}phenyl)methacrylamide] (abbreviation: PTPDMA) or poly[N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)benzidine] (abbreviation: poly- TPD) can also be used.

By providing a hole injection layer, a high hole transport property can be achieved to enable a light emitting element to have a low driving voltage.

The hole transport layer 112 is a layer containing a substance having a hole transport property. Examples of the substance having a hole transport property are aromatic amine compounds such as 4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB), N,N'-bis(3-methylphenyl)-N "N'-diphenyl-[1,1'-biphenyl]-4,4'-diamine (abbreviation: TPD), 4,4',4"-tris(N,N-diphenylamino)triphenylamine (abbreviation: TDATA), 4,4',4"-Tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine (abbreviation: MTDATA), 4,4'-Bis[N-(spiro-9,9'-bifluoren-2- yl)-N-phenylamino]biphenyl (abbreviation: BSPB), 4-phenyl-4'-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP) and the like. The substances mentioned here have a high hole transport property and are mainly those with a hole mobility of 10 ^-6 cm ² /Vs or more. An organic compound given as an example of the substance having the hole transport property in the composite material described above can also be used for the hole transport layer 112. A high molecular weight compound such as poly(N-vinylcarbazole) (abbreviation: PVK) or poly(4-vinyltriphenylamine) (abbreviation: PVTPA) can also be used. It should be noted that the layer containing a substance having a hole transport property is not limited to a single layer and may be a stack of two or more layers containing each of the above substances.

The light-emitting layer 113 is a layer containing the first phosphorescent compound and the second phosphorescent compound. Since the light-emitting layer 113 has a structure similar to that described in Embodiment 1, the light-emitting element in this embodiment can have extremely high emission efficiency. Reference is made to Embodiment 1 for the main structures of the light emitting layer 113.

There is no particular limitation on the materials used as the first phosphorescent compound and the second phosphorescent compound yy in the light-emitting layer 1q13 as long as they have the relationship described in Embodiment 1. The following can be cited as examples of the first phosphorescent compound and the second phosphorescent compound.

The examples are an organometallic iridium complex with a 4H-triazole skeleton, such as Tris{2-[5-(2-methylphenyl)-4-(2,6-dimethylphenyl)-4H-1,2,4-triazol-3-yl- κN ² ]phenyl-κC}iridium(III) (Abbreviation: Ir(mpptz-dmp) ₃ ), Tris(5-methyl-3,4-diphenyl-4H-1,2,4-triazolato)iridium(III) ( Abbreviation: Ir(Mptz) ₃ ) or Tris[4-(3-biphenyl)-5-isopropyl-3-phenyl-4H-1,2,4-triazolato]iridium(III) (Abbreviation: Ir(iPrptz-3b) ₃ ); an organometallic iridium complex with a 1H-triazole skeleton, such as tris[3-methyl-1-(2-methylphenyl)-5-phenyl-1H-1,2,4-triazolato]iridium(III) (abbreviation: Ir(Mptz1-mp ) ₃ ) or Tris(1-methyl-5-phenyl-3-propyl-1H-1,2,4-triazolato)iridium(III) (abbreviation: Ir(Prptz1-Me) ₃ ); an organometallic iridium complex with an imidazole skeleton, such as fac-Tris[1-(2,6-diisopropylphenyl)-2-phenyl-1H-imidazol]iridium(III) (abbreviation: Ir(iPrpmi) ₃ ) or Tris[3-(2 ,6-dimethylphenyl)-7-methylimidazo[1,2-f]phenanthridinato]iridium(III) (abbreviation: Ir(dmpimpt-Me) ₃ ); and an organometallic iridium complex in which a phenylpyridine derivative having an electron-withdrawing group is a ligand, such as bis[2-(4',6'-difluorophenyl)pyridinato-N,C ^2' ]iridium(III)tetrakis(1-pyrazolyl)borate (Abbreviation: Flr6), Bis[2-(4',6'-difluorophenyl)pyridinato-N,C ^2' ]iridium(III)picolinate (Abbreviation: Flrpic), Bis{2-[3',5'-bis (trifluoromethyl)phenyl]pyridinato-N,C ² }iridium(III)picolinate (abbreviation: Ir(CF ₃ ppy) ₂ (pic)) or bis[2-(4',6'-difluorophenyl)pyridinato-N,C ^2' ]iridium(III)acetylacetonate (abbreviation: Flracac). These are compounds that emit blue phosphorescence and have an emission peak at 440 nm to 520 nm. Among the above compounds, an organometallic iridium complex having a polyazole skeleton such as a 4H-triazole skeleton, a 1H-triazole skeleton or an imidazole skeleton has a high hole-trapping property. Therefore, it is preferable that each of these compounds, which is used as the first phosphorescent compound in the light-emitting element of an embodiment of the present invention, the first light-emitting layer is provided closer to the cathode than the second light-emitting layer and that the second light-emitting layer is a Hole transport property (in particular the second host material is a hole transport material), in which case a recombination region of the carrier can be easily controlled to be in the first light-emitting layer. It should be noted that an organometallic iridium complex with a 4H-triazole skeleton has excellent reliability and emission efficiency and is therefore particularly preferred.

Other examples include an organometallic iridium complex with a pyrimidine skeleton, such as tris(4-methyl-6-phenylpyrimidinato)iridium(III) (abbreviation: Ir(mppm) ₃ ), tris(4-t-butyl-6-phenylpyrimidinato)iridium (III) (Abbreviation: Ir(tBuppm) ₃ ), (Acetylacetonato)bis(6-methyl-4-phenylpyrimi-dinato)iridium(III) (Abbreviation: Ir(mppm) ₂ (acac)), (Acetylacetonato)bis( 6-tert-butyl-4-phenylpyri-midinato)iridium(III) (abbreviation: Ir(tBuppm) ₂ (acac)), (acetylacetonato)bis[6-(2-norbornyl)-4-phenylpyrimidinatojiridium(III) (abbreviation : Ir(nbppm) ₂ (acac)), (acetylacetonato)bis[5-methyl-6-(2-methylphenyl)-4-phenylpyrimidinato]iridium(III) (abbreviation: Ir(mpmppm) ₂ (acac)) or ( Acetylacetonato)bis(4,6-diphenylpyrimidinato)iridium(III) (abbreviation: Ir(dppm) ₂ (acac)); an organometallic iridium complex with a pyrazine skeleton, such as (acetylacetonato)bis(3,5-dimethyl-2-phenylpyrazinato)iridium(III) (abbreviation: Ir(mppr-Me) ₂ (acac)) or (acetylacetonato)bis(5-isopropyl -3-methyl-2-phenylpyrazinato)iridium(III) (abbreviation: Ir(mppr-iPr) ₂ (acac)); an organometallic iridium complex with a pyridine skeleton, such as tris(2-phenylpyridinato-N,C ² )iridium(III) (abbreviation: Ir(ppy) ₃ ), bis(2-phenylpyridinato-N,C ^2' )iridium(III) acetylacetonate (Abbreviation: Ir(ppy) ₂ (acac)), Bis(benzo[h]quinolinato)iridium(III)acetylacetonate (Abbreviation: Ir(bzq) ₂ (acac)), Tris(benzo[h]quinolinato)iridium(III ) (abbreviation: Ir(bzq) ₃ ), tris(2-phenylquinolinato-N,C ^2' )iridium(III) (abbreviation: Ir(pq) ₃ ) or bis(2-phenylquinolinato-N,C ^2' )iridium (III)acetylacetonate (abbreviation: Ir(pq) ₂ (acac)); and a rare earth metal complex, such as tris(acetylacetonato)(monophen-anthroline)terbium(III) (abbreviation: Tb(acac) ₃ (Phen)). These are mainly compounds that emit green phosphorescence and have an emission peak at 500 nm to 600 nm. Among the above compounds, an organometallic iridium complex having a diazine skeleton such as a pyrimidine skeleton or a pyrazine skeleton has a low hole trapping property and a high electron trapping property. Therefore, it is preferable that each of these compounds is used as the first phosphorescent compound in the light-emitting element of an embodiment of the present invention, that the first light-emitting layer is provided closer to the anode than the second light-emitting layer, and that the second light-emitting layer has an electron transport property (in particular, that the second host material is an electron transport material), whereby in this case a recombination region of the carriers can be easily controlled to be in the first light-emitting layer. It should be noted that an organometallic iridium complex with a pyrimidine skeleton has a distinctive high reliability and emission efficiency and is therefore particularly preferred.

Still other examples are an organometallic iridium complex with a pyrimidine skeleton, such as Bis[4,6-bis(3-methylphenyl)pyrimidinato](diisobutylylmethano)iridium(III) (abbreviation: Ir(5mdppm) ₂ (dibm)), Bis[4, 6-bis(3-methylphenyl)pyrimidinato](dipivaloylmethanato)iridium(III) (abbreviation: Ir(5mdppm) ₂ (dpm)) or bis[4,6-di(naphthalen-1-yl)pyrimidinato](dipivaloylmetha-nato )iridium(III) (abbreviation: Ir(d1npm) ₂ (dpm)); an organometallic iridium complex with a pyrazine skeleton, such as (acetylacetonato)bis(2,3,5-triphenylpyrazinato)iridium(III) (abbreviation: Ir(tppr) ₂ (acac)), bis(2,3,5-triphenylpyrazinato)(dipivaloylmethanato )iridium(III) (Abbreviation: Ir(tppr) ₂ (dpm)) or (acetylacetonato)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III) (Abbreviation: Ir(Fdpq) ₂ (acac)); an organometallic iridium complex with a pyridine skeleton, such as tris(1-phenylisoquinolinato-N,C ^2' )iridium(III) (abbreviation: Ir(piq) ₃ ) or bis(1-phenylisoquinolina-to-N,C ^2' )iridium( III)acetylacetonate (abbreviation: Ir(piq) ₂ (acac)); a platinum complex, such as 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrinplatinum(II) (abbreviation: PtOEP); and a rare earth metal complex, such as Tris(1,3-diphenyl-1,3-propanedionato)(monophenanthroline)europium(III) (abbreviation: Eu(DBM) ₃ (Phen)) or Tris[1-(2-thenoyl)-3 ,3,3-trifluoroacetonato](mono-phenanthroline)europium(III) (abbreviation: Eu(TTA) ₃ (Phen)). These are compounds that emit red phosphorescence and have an emission peak at 600 nm to 700 nm. Among the above materials, an organometallic iridium complex having a diazine skeleton such as a pyrimidine skeleton or a pyrazine skeleton has a low hole easy property and a high electron capture property. Therefore, it is preferred that an organometallic iridium complex having a diazine skeleton is used as the second phosphorescent compound, the first light-emitting layer is provided closer to the cathode than the second light-emitting layer, and the second light-emitting layer has a hole transport property (particularly that the second host material is a hole transport material), whereby a recombination region of the carriers can be easily controlled to be in the first light-emitting layer. It should be noted that an organometallic iridium complex with a pyrimidine skeleton has distinctively high reliability and emission efficiency and is therefore particularly preferred. Furthermore, since an organometallic iridium complex having a pyrazine skeleton can provide red light emission with preferential chromaticity, use of the organometallic iridium complex in a white light emitting element improves a color rendering property of the white light emitting element.

It is also possible to select a first phosphorescent material and a second phosphorescent material described with respect to Embodiment 1 from known phosphorescent materials in addition to the above phosphorescent materials.

It should be noted that instead of the phosphorescent compounds (the first phosphorescent compound 113a and the second phosphorescent compound 113b), materials showing thermally activated delayed fluorescence, that is, thermally activated delayed fluorescence (TADF) materials, can be used. Here, the term “delayed fluorescence” refers to light emission with a spectrum similar to that of normal fluorescence and an extremely long lifespan. The service life is 10 ^-6 seconds or more, preferably 10 ^-3 seconds or more. Specific examples of thermally activated delayed fluorescent materials include a fullerene, a derivative thereof, an acridine derivative such as proflavine and eosin. In addition, a metal-containing porphyrin can be used, such as a porphyrin containing magnesium (Mg), zinc (Zn), cadmium (Cd), tin (Sn), platinum (Pt), indium (In) or palladium (Pd). Examples of the metal-containing porphyrin include a protoporphyrin-stannous fluoride complex (abbreviation: SnF ₂ (Proto IX)), a mesoporphyrin-stannous fluoride complex (abbreviation: SnF ₂ (Meso IX)), a hematoporphyrin-stannous fluoride complex (abbreviation: SnF ₂ (Hemato IX)), a coproporphyrin tetramethyl ester-stannous fluoride complex (abbreviation: SnF ₂ (Copro III-4Me)), an octaethylporphyrin-stannous fluoride complex (abbreviation: SnF ₂ (OEP)), an etioporphyrin-stannous fluoride complex (abbreviation: SnF ₂ (Etio I)) and an octaethylporphyrin-platinum chloride complex (abbreviation: PtCl ₂ (OEP)). Alternatively, a heterocyclic compound containing a π-electron-rich heteroaromatic ring and a π-electron-poor heteroaromatic ring can be used, such as 2-(biphenyl-4-yl)-4,6-bis(12-phenylindolo[2,3-α] carbazol-11-yl)-1,3,5-triazine (abbreviation: PIC-TRZ). It should be noted that a material in which the π-electron-rich heteroaromatic ring is directly bonded to the π-electron-poor heteroaromatic ring is particularly preferred because the donor property of the π-electron-rich heteroaromatic ring and the acceptor property of the π-electron-poor heteroaromatic ring both are increased and the energy difference between the S ₁ level and the T ₁ level becomes small.

There is no particular limitation on the materials that can be used as the first and second host materials; A variety of carrier transport materials can be selected and suitably combined so that one in the 1A until 1C element structure shown is obtained.

The following are examples of the host material with an electron transport property: a metal complex such as bis(10-hydroxybenzo[h]quinolinato)beryllium(lI) (abbreviation: BeBq ₂ ), bis(2-methyl-8-quinolinolato)(4-phenylphenolato) aluminum(III) (abbreviation: BAlq), bis(8-quinolinola-to)zinc(II) (abbreviation: Znq), bis[2-(2-benzoxazolyl)phenolato]zinc(II) (abbreviation: ZnPBO) or Bis [2-(2-benzothiazolyl)phenolato]zinc(II) (abbreviation: ZnBTZ); a heterocyclic compound with a polyazole skeleton, such as 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation: PBD), 3-(4-biphenylyl)-4-phenyl -5-(4-tert-butylphenyl)-1,2,4- triazole (abbreviation: TAZ), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene (abbreviation: OXD-7), 9-[4-( 5-phenyl-1,3,4-oxadiazol-2-yl)phenyl]-9H-carbazole (abbreviation: CO11), 2,2',2"-(1,3,5-benzenetriyl)tris(1-phenyl -1H-benzimidazole) (abbreviation: TPBI) or 2-[3-(Dibenzothiophen-4-yl)phenyl]-1-phenyl-1H-benzimidazole (abbreviation: mDBTBIm-II); a heterocyclic compound with a diazine skeleton, such as 2 -[3-(Dibenzothiophen-4-yl)phenyl)dibenzo[f,h]quinoxaline (abbreviation: 2mDBTPDBq-II), 2-[3'-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f ,h]quinoxaline (abbreviation: 2mDBTBPDBq-II), 2-[3'-(9H-carbazol-9-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline (abbreviation: 2mCzBPDBq), 4,6- Bis[3-(phenanthren-9-yl)phenyl]pyrimidine (abbreviation: 4.6mPnP2Pm) or 4,6-bis[3-(4-dibenzothienyl)phenyl]pyrimidine (abbreviation: 4.6mDBTP2Pm-II); and one heterocyclic compound with a pyridine skeleton, such as 3,5-bis[3-(9H-carbazol-9-yl)phenyl]pyridine (abbreviation: 35DCzPPy) or 1,3,5-tri[3-(3-pyridyl)phenyl] benzene (abbreviation: TmPyPB). Among the above materials, a heterocyclic compound having a diazine skeleton and a heterocyclic compound having a pyridine skeleton have high reliability and are therefore preferred. In particular, a heterocyclic compound having a diazine (pyrimidine or pyrazine) skeleton has a high electron transport property to contribute to a reduction in driving voltage.

The following are examples of the host material with a hole transport property: a compound with an aromatic amine skeleton, such as 4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB), N,N'-Bis (3-methylphenyl)-N,N'-diphenyl-[1,1'-biphenyl]-4,4'-diamine (abbreviation: TPD), 4,4'-Bis[N-(spiro-9,9' -bifluoren-2-yl)-N-phenylamino]biphenyl (abbreviation: BSPB), 4-phenyl-4'-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP), 4-phenyl-3'-( 9-phenylfluoren-9-yl)triphenylamine (abbreviation: mBPAFLP), 4-phenyl-4'-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBA1BP), 4,4'-diphenyl-4 "-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBBi1BP), 4-(1-naphthyl)-4'-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBANB), 4,4'-Di(1-naphthyl)-4"-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBNBB), 9,9-Dimethyl-N-phenyl-N- [4-(9-phenyl-9H-carbazol-3-yl)phenyl]fluoren-2-amine (abbreviation: PCBAF) or N-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl )phenyl]spiro-9,9'-bifluoro-ren-2-amine (abbreviation: PCBASF); a compound with a carbazole skeleton, such as 1,3-bis(N-carbazolyl)benzene (abbreviation: mCP), 4,4'-di(N-carbazolyl)biphenyl (abbreviation: CBP), 3,6-bis(3, 5-diphenylphenyl)-9-phenylcarbazole (abbreviation: CzTP) or 3,3'-bis(9-phenyl-9H-carbazole) (abbreviation: PCCP); a compound with a thiophene skeleton, such as 4,4',4"-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation: DBT3P-II), 2,8-diphenyl-4-[4-( 9-phenyl-9H-fluoren-9-yl)phenyl]dibenzothiophene (abbreviation: DBTFLP-III), or 4-[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-6-phenyldibenzothiophene (abbreviation : DBTFLP-IV); and a compound with a furan skeleton, such as 4,4',4"-(benzene-1,3,5-triyl)tri(dibenzofuran) (abbreviation: DBF3P-II) or 4-{3- [3-(9-Phenyl-9H-fluoren-9-yl)phenyl]phenyl }dibenzofuran (abbreviation: mmDBFFLBi-II). Among the above materials, a compound having an aromatic amine skeleton and a compound having a carbazole skeleton are preferred because these compounds are very reliable and have high hole transport properties to help reduce the driving voltage

Host materials can be selected from known substances, as well as the above host materials. It should be noted that as the host materials, substances having a triplet level (energy gap between a ground state and a triplet excited state) larger than that of the phosphorescent compound are preferably selected. It is preferred that these host materials do not have an absorption spectrum in the blue wavelength range. In particular, an absorption edge of the absorption spectrum is preferably 440 nm or less.

To form the light-emitting layer 113 having the structure described above, co-evaporation may be used by a vacuum evaporation method, or alternatively, an ink-jet method, a spin-coating method, a dipping method, or the like using a mixed solution.

The electron transport layer 114 is a layer containing a substance having an electron transport property. For example, a layer containing a metal complex with a quinoline skeleton or a benzoquinolinate skeleton, such as Tris(8-quinolinolato)aluminum (abbreviation: Alq), Tris(4-methyl-8-quinolinolato)aluminum (abbreviation: Almq ₃ ), Bis( 10-hydroxyben-zo[h]quinolinato)beryllium (abbreviation: BeBq ₂ ) or bis(2-methyl-8-quinolinolato)(4-phenylphe-nolato)aluminum (abbreviation: BAlq) or the like. be used. Alternatively, a metal complex can be formed with an oxal-based or a thiazole-based ligand, such as bis[2-(2-hydroxyphenyl)benzoxazolato]zinc (abbreviation: Zn(BOX) ₂ ) or bis[2-(2-hydroxyphenyl)benzothiazolato ]zinc (abbreviation: Zn(BTZ) ₂ ) or the like can be used. In addition to the metal complexes, such as 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation: PBD), 1,3-bis[5-(p-tert-butylphenyl )-1,3,4-oxadiazol-2-yl]benzene (abbreviation: OXD-7), 3-(4-Biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4 -triazole (abbreviation: TAZ), bathophenanthroline (abbreviation: BPhen), bathocuproin (Abbreviation: BCP) or the like can also be used. The substances mentioned here have high electron transport properties and are mainly those with an electron mobility of 10 ^-6 cm ² /Vs or more. It should be noted that any of the host materials having electron properties described above can be used for the electron transport layer 114.

Furthermore, the electron transport layer 114 is not limited to a single layer and may be a stack of two or more layers containing each of the above substances.

A layer which controls the transport of the electron carriers can be provided between the electron transport layer and the light-emitting layer. This is a layer formed by adding a small amount of a substance having a high electron capture property to a material having a high electron transport property as described above, and the layer is capable of adjusting the carrier balance by suppressing the transport of electron carriers becomes. Such a structure is very effective in preventing a problem (such as a reduction in the life of the element) arising when electrons are passed through the light-emitting layer.

In addition, the electron injection layer 115 may be provided in contact with the second electrode 102 between the electron transport layer 114 and the second electrode 102. For the electron injection layer 115, an alkali metal, an alkaline earth metal, or a compound thereof, such as lithium fluoride (LiF), cesium fluoride (CsF), or calcium fluoride (CaF ₂ ), can be used. For example, a layer formed using a substance having an electron transport property and containing an alkali metal, an alkaline earth metal, or a compound thereof may be used. It should be noted that a layer formed using a substance having an electron transport property and containing an alkali metal or an alkaline earth metal is preferably used as the electron injection layer 115, in which case the electron injection from the second electrode 102 is efficiently performed.

For the second electrode 102, any metal, alloy, electrically conductive compound, and mixtures thereof having a low work function (particularly a work function of 3.8 eV or less) or the like may be used. Specific examples of such a cathode material are elements belonging to groups 1 and 2 of the periodic table, such as alkali metals (e.g. lithium (Li) and cesium (Cs)), magnesium (Mg), calcium (Ca) and strontium (Sr ), alloys of these (e.g. MgAg and AlLi), rare earth metals such as europium (Eu) and ytterbium (Yb), alloys of these and the like. However, when the electron injection layer is provided between the second electrode 102 and the electron transport layer, a variety of conductive materials such as Al, Ag, ITO or indium oxide-tin oxide containing silicon or silicon oxide may be used for the second electrode 102, regardless of the work function . Films of these electrically conductive materials can be formed by a sputtering process, an ink jet process, a spin coating process, or the like.

Furthermore, any of a variety of methods can be used to form the EL layer 103, regardless of whether it is a wet method or a dry method. For example, a vacuum evaporation process, an ink jet process, a spin coating process, or the like can be used. Different manufacturing processes can be used for the electrodes or the layers.

In addition, the electrode may be manufactured by a wet method using a sol-gel method or by a wet method using a paste of a metal material. Alternatively, the electrode may be manufactured by a dry process such as a sputtering process or a vacuum evaporation process.

In the light-emitting element having the structure described above, current flows due to a potential difference between the first electrode 101 and the second electrode 102, and holes and electrons recombine in the light-emitting layer 113 containing a substance having a high light-emitting property, so that light is emitted . That is, a light emitting region is formed in the light emitting 113.

The light emission is extracted by one or both of the first electrode 101 and the second electrode 102. Therefore, one or both of the first electrode 101 and the second electrode 102 are light-transmissive electrodes. In the case where only the first electrode 101 is a transparent electrode, the Light emission extracted by the first electrode 101. In the case where only the second electrode 102 is a transparent electrode, the light emission is extracted by the second electrode 102. In the case where both the first electrode 101 and the second electrode 102 are light-transmitting electrodes, the light emission is extracted by the first electrode 101 and the second electrode 102.

The structure of the layers provided between the first electrode 101 and the second electrode 102 is not limited to the structure described above. Preferably, a light-emitting region in which holes and electrons recombine is disposed away from the first electrode 101 and the second 102 so that quenching due to the proximity of the light-emitting region and a metal and carrier injection layers used for the electrodes can be prevented.

In order to suppress the transfer of energy from an exciton generated in the light-emitting layer, the hole transport layer and the electron transport layer in contact with the light-emitting layer 113, particularly a carrier transport layer in contact with a side closer to the light-emitting region in the light-emitting layer 113 is formed using a substance having a wider band gap than the light-emitting substance of the light-emitting layer or the emission center substance contained in the light-emitting layer.

A light-emitting element in this embodiment is preferably fabricated on a substrate made of glass, plastic or the like. As a way of stacking the layers on the substrate, the layers may be stacked sequentially from the first electrode 101 side or sequentially from the second electrode 102 side. Although one light-emitting element can be formed on one substrate, in a light-emitting device, a plurality of light-emitting elements can be formed on one substrate. When a plurality of light-emitting elements as described above are formed on a substrate, a lighting device in which the elements are separated from each other or a passive matrix light-emitting device can be manufactured. A light emitting element can be formed on an electrode electrically connected to a thin film transistor (TFT) formed on a substrate made of glass, plastic or the like, so that an active matrix light emitting device can be manufactured in which the TFT Control of the light-emitting element controls. It should be noted that there is no particular limitation on the structure of the TFT, which may be a staggered TFT or an inverted staggered TFT. In addition, the crystallinity of a semiconductor used for the TFT is also not particularly limited; an amorphous semiconductor or a crystalline semiconductor can be used. In addition, a driver circuit formed in a TFT substrate will be formed with an n-type TFT and a p-type TFT or either an n-type TFT or a p-type TFT.

It should be noted that this embodiment can be combined with any other embodiment as appropriate.

Embodiment 3

In this embodiment, a light emitting device using the light emitting element described in Embodiments 1 and 2 will be described.

In this embodiment, the light emitting device using the light emitting element described in Embodiments 1 and 2 will be described with reference to 4A and 4B described. It should be noted that 4A is a top view of the light-emitting device and 4B a cross section along lines AB and CD in 4A . This light emitting device includes a driving circuit portion (source line driving circuit) 601, a pixel portion 602, and a driving circuit portion (gate line driving circuit) 603, which control the light emission of the light emitting element and are shown in broken lines. Further, reference numeral 604 denotes a sealing substrate; 625 a desiccant; 605 a sealing material; and 607 a space surrounded by the sealing material 605.

Reference numeral 608 denotes a wiring for transmitting signals introduced into the source line driving circuit 601 and the gate line driving circuit 603 and for receiving signals such as a video signal, a timing signal, a start signal and a reset signal an FPC (flexible printed circuit board) 609, which serves as an external input terminal. Although only the FPC is shown here, it can a printed circuit board (PWB) must be attached to the FPC. The light-emitting device of the present specification includes in this category not only the light-emitting device itself but also the light-emitting device provided with the FPC or PWB.

A cross-sectional structure is presented below with reference to 4B described. The driver circuit area and the pixel area are formed on an element substrate 610; the source line driver circuit 601, which is a driver circuit region, and one of the pixels in the pixel region 602 are shown here.

As the source line driver circuit 601, a CMOS circuit in which an n-channel TFT 623 and a p-channel TFT 624 are combined is formed. In addition, the driver circuit may be formed with any of a variety of circuits such as a CMOS circuit, a PMOS circuit, or an NMOS circuit. Although an integrated circuit in which the driver circuit is formed on the substrate is shown in this embodiment, the driver circuit does not necessarily have to be formed on the substrate and the driver circuit may not be formed on the substrate outside.

The pixel region 602 includes a plurality of pixels formed each having a switching TFT 611, a current control TFT 612, and a first electrode 613 electrically connected to a drain of the current control TFT 612. It should be noted that to cover an end portion of the first electrode 613, an insulator 614 is formed, for which a positive photosensitive acrylic resin film is used here.

To improve coverage, the insulator 615 is formed to have a curved surface, with the curve formed at the upper or lower end portion. For example, in the case where the positive photosensitive acrylic resin is used as a material for the insulator 614, only the upper end portion of the insulator 614 is preferably formed with a curved surface having a radius of curvature (0.2 μm to 3 μm). As the insulator 614, either a negative photosensitive resin or a positive photosensitive resin can be used.

An EL layer 616 and a second electrode 617 are formed on the first electrode 613. Here, as a material used for the first electrode 613 serving as an anode, a material having a high work function is preferably used. For example, a single-layer film may be made of an ITO film, an indium tin oxide film containing silicon, an indium oxide film containing zinc oxide at 2% to 20% by weight, a titanium nitride film, a chromium film, a tungsten film, etc Zn film, a Pt film or the like, a stack of a titanium nitride film and a film containing aluminum as a main component, a stack of three layers of a titanium nitride film, a film containing aluminum as a main component and a titanium nitride film or the like can be used. The stacked layer structure enables low wiring resistance, preferential ohmic contact, and function as an anode.

In addition, the EL layer 616 is formed by any of a variety of methods such as an evaporation method using an evaporation mask, an ink jet method, and a spin coating method. The EL layer 616 has a structure similar to that described in Embodiments 1 and 2. Further, as another material included in the EL layer 616, any low molecular weight compound and high molecular weight compound (including oligomers and dendrimers) can be used.

As a material used for the second electrode 617 formed over the EL layer 616 and serving as a cathode, a material having a low work function (e.g. Al, Mg, Li, Ca) may preferably be used or an alloy or a compound thereof, such as MgAg, Mgl, or AlLi). In the case that light generated in the EL layer 616 is passed through the second electrode 617, a stack of a thin metal film or foil and a transmissive conductive film (e.g. ITO, indium oxide containing zinc oxide) is preferably used 2% by weight to 20% by weight, indium tin oxide, containing silicon or zinc oxide (ZnO)) is preferably used for the second electrode 617.

It should be noted that the light emitting element is formed with the first electrode 613, the EL layer 616 and the second electrode 617. The light-emitting element is the light-emitting element described in Embodiments 1 and 2. In the light emitting device of this embodiment, the pixel area including a plurality of light emitting elements Ten includes both the light-emitting element described in Embodiments 1 and 2 and a light-emitting element having a different structure.

Further, the sealing substrate 604 is attached to the element substrate 610 via the sealing material 605, so that a light-emitting element 618 is provided in the space 607 surrounded by the element substrate 610, the sealing substrate 604 and the sealing material 605. The space 607 may be filled with a filler, or may be filled with an inert gas (such as nitrogen or argon) or the sealing material 605. It is preferable that the sealing substrate is provided with a recessed area and that the desiccant 625 is provided in the recessed area so that deterioration due to the influence of moisture can be suppressed.

An epoxy-based resin or a glass frit is preferably used as the sealing material 605. It is preferred that such a material does not transmit moisture or oxygen as much as possible. As the sealing substrate 604, a glass substrate, a quartz substrate, or a plastic substrate made of fiberglass reinforced plastic (FRP), poly(vinyl fluoride) (PVF), polyester, acrylic resin, or the like may be used.

As described above, the light emitting device using the light emitting element described in Embodiments 1 and 2 can be obtained.

The light-emitting device in this embodiment is manufactured using the light-emitting element described in Embodiments 1 and 2, and therefore can have advantageous characteristics. In particular, since the light emitting element described in Embodiments 1 and 2 has a high emission efficiency, the light emitting device can have reduced power consumption. In addition, since the light-emitting element has a low driving voltage, the light-emitting device can be operated at a low voltage.

Although an active matrix light emitting device is described in this embodiment as described above, a passive matrix light emitting device can be manufactured. The 5A and 5B show a passive matrix light emitting device made using the present invention. 5A shows a perspective view of the light emitting device and 5B shows a cross section along line XY in 5A . In the 5A and 5B an EL layer 955 is provided on a substrate 951 between an electrode 952 and an electrode 956. An end region of the electrode 952 is covered with an insulation layer 953. In addition, a separation layer 954 is provided on the insulation layer 953. The side walls of the separation layer 954 are beveled so that the distance between the two side walls gradually tapers towards the surface of the substrate. In other words, a cross section along the short side direction of the partition layer 954 is trapezoidal, and the lower side (a side which is in the same direction as a flat direction of the insulation layer 953 and is in contact with the insulation layer 953) is shorter than the upper side (a side which is in the same direction as the flat direction of the insulating layer 953 and is not in contact with the insulating layer 953). The separation layer 954 thus provided can prevent failure of the light emitting element due to static electricity or the like. The passive matrix light-emitting device can also be operated with low power consumption, including the light-emitting element of Embodiments 1 and 2, which can be operated at low voltage. Further, the light emitting device can have high reliability by including the light emitting element described in Embodiments 1 and 2.

Further, in order to provide a full-color display, a coloring layer or a color conversion layer may be provided in a light path through which the light is transmitted from the light-emitting element to the outside of the light-emitting device. An example of a light emitting device in which full color display is achieved using a color layer and the like is shown in Figs 6A and 6B shown. In 6A is a substrate 1001, a base insulation film 1002, a gate insulation film 1003, gate electrodes 1006, 1007 and 1008, a first interlayer insulation film 1020, a second interlayer insulation film 1021, a peripheral region 1042, a pixel region 1040, a driver circuit region 1041, first electrodes 1024W, 1024R, 1024G and 1024B of the light emitting elements, a partition wall 1025, an EL layer 1028, a second electrode 1029 of the light emitting elements, a sealing substrate 1031 and sealant 1032 are shown. Furthermore, there are color layers (a red color layer 1034R, a green color layer 1034G and a blue color layer 1034B) provided on a transparent base material 1033. Furthermore, a black layer (a black matrix) 1035 may be additionally provided. The transparent base material 1033, which is provided with color layers and the black layer, is arranged on the substrate 1001 and fixed thereon. It should be noted that the color layers and the black layer are covered with an overlayer 1036. In this embodiment, light emitted from some of the light-emitting layers is not passed through the color layers, while light emitted from the other of the light-emitting layers is passed through the color layers. Since light that does not pass through the color layers is white and light that passes through one of the color layers is red, blue or green, an image can be reproduced using pixels of the four colors.

The light emitting device described above is a light emitting device having a structure in which light is extracted from the side of the substrate 1001 on which the TFTs are formed (a bottom emission structure), but may also be a light emitting device having a structure in which Light is extracted from the side of the seal substrate 1031 (a top emission structure). 7 shows a cross section of a light-emitting device with a top emission structure. In this case, a substrate that does not transmit light may be used as the substrate 1001. The process up to the step of forming a connection electrode connecting the TFT and the anode of the light emitting element is carried out in a similar manner to that of the light emitting device having a bottom emission structure. Subsequently, a third interlayer insulation film 1037 is formed to cover an electrode 1022. The third interlayer insulation film 1037 may have a planarizing function. The third interlayer insulation film 1037 may be formed using a material similar to that of the second interlayer insulation film, and may alternatively be formed using another known material.

The first electrodes 1024W, 1024R, 1024G and 1024B of the light emitting elements serve here as an anode, but may also serve as a cathode. Furthermore, in the case of a light-emitting device with a top emission structure, as in 7 shown, the first electrodes are preferably reflective electrodes. The EL layer 1028 is formed with a similar structure to the structure described in Embodiments 1 and 2, whereby white light emission can be obtained. As the structure with which the emission of white light can be obtained, in the case where two EL layers are used, a structure with which blue light is obtained from a light-emitting layer in one of the EL layers is adopted and orange light is obtained from a light-emitting layer of the other of the EL layers; a structure in which blue light is obtained from a light-emitting layer of one of the EL layers and red light and green light are obtained from a light-emitting layer of the other of the EL layers; and the like can be cited. Further, in the case where three EL layers are used, red light, green light and blue light can be obtained from the respective light-emitting layers, so that the light-emitting element that emits white light can be obtained. It is not necessary to state that the structure in which white light emission is obtained is not limited to this as long as the structure described in Embodiments 1 and 2 is used.

The color layers are each provided in a light path through which light is transmitted from the light-emitting element to the outside of the light-emitting device. In the case of the light emitting device having a bottom emission structure as in 6A As shown, the color layers 1034R, 1034G and 1034B may be provided on the transparent base material 1033 and then attached to the substrate 1001. The color layers may be provided between the gate insulation film 1003 and the first interlayer insulation film 1020, as shown in 6B shown. In the case of a top issue structure, as in 7 As shown, sealing can be performed with the sealing substrate 1031 on which the color layers (the red color layer 1034R, the green color layer 1034G and the blue color layer 1034B) are provided. The sealing substrate 1031 may be provided with the black layer (black matrix) 1035 disposed between the pixels. The color layers (the red color layer 1034R, the green color layer 1034G and the blue color layer 1034B) and the black layer (the black matrix) 1035 may be covered with a top layer 1036. It should be noted that a transparent substrate is used as the sealing substrate 1031.

When voltage is applied between the pair of electrodes of the organic light-emitting element thus obtained, a white light-emitting region 1044W can be obtained. Additionally A red light emitting region 1044W, a blue light emitting region 1044B and a green light emitting region 1044G can be obtained using the color layers. The light emitting device of this embodiment includes the light emitting element described in Embodiments 1 and 2; therefore, a low power consumption light emitting device can be obtained.

Although an example in which a full-color display is achieved using the four colors red, green, blue and white is described here, there is no particular limitation, and a full-color display using the three colors red, green and blue can also be performed.

This embodiment can be freely combined with any other embodiment.

Embodiment 4

In this embodiment, an example in which the light emitting element described in Embodiments 1 and 2 is used for a lighting device will be described with reference to FIG 8A and 8B described. 8B shows a top view of the lighting device and 8A shows a cross section along the line ef in 8B .

In the lighting device in this embodiment, a first electrode 401 is formed on a substrate 400, which is a support and has a light-transmissive property. The first electrode 401 corresponds to the first electrode 101 in Embodiment 3.

An auxiliary electrode 402 is provided on the first electrode 401. Since the light emission is extracted through the first electrode 401 side in the example given in this embodiment, the first electrode 401 is formed using a material having a light-transmissive property. The auxiliary electrode 402 is provided to compensate for the low conductivity of the material having a light-transmitting property and has a function of suppressing the luminance unevenness in a light emitting surface due to a voltage loss caused by the high resistance of the first electrode 401. The auxiliary electrode 402 is formed using a material having at least a higher conductivity than the material of the first electrode 401, and is preferably formed using a material having a high conductivity such as aluminum. It should be noted that the surfaces of the auxiliary electrode 402 other than a portion thereof which is in contact with the first electrode 401 are preferably covered with an insulating layer. This is to suppress light emission on the upper portion of the auxiliary electrode 402, which cannot be extracted, to reduce reactive current and to suppress reduction in power efficiency. It should be noted that a pad 412 for applying a voltage to a second electrode 402 may be formed simultaneously with the formation of the auxiliary electrode 402.

An EL layer 403 is formed on the first electrode 401 and the auxiliary electrode 402. The EL layer 403 has the structure described in Embodiments 1 and 2. Regarding the structure, reference is made to these descriptions. It should be noted that the EL layer 403 is preferably formed slightly larger than the first electrode 401 when viewed from above, so in this case the EL layer 403 can also serve as an insulating layer preventing a short circuit between the first electrode 401 and the second electrode 404 prevented.

The second electrode 404 is formed to cover the EL layer 403. The second electrode 404 corresponds to the second electrode 102 in Embodiment 3 and has a similar structure. In this embodiment, since the light emission is extracted through the first electrode 401 side, it is preferable that the second electrode 404 is formed using a material having a high reflectivity. In this embodiment, the second electrode 404 is connected to the pad 412, thereby applying voltage.

As described above, the lighting device described in this embodiment includes a light emitting element including the first electrode 401, the EL layer 403, and the second electrode 404 (and the auxiliary electrode 402). Since the light-emitting element is a light-emitting element with high emission efficiency, the lighting device in this embodiment can be a lighting device having low power consumption. Since the light-emitting element further is a high-reliability light-emitting element, the lighting device of this embodiment can be a high-reliability lighting device.

The light emitting element having the above structure is attached to a sealing substrate 407 via sealing materials 405 and 406, and sealing is performed, thereby completing the lighting device. It is possible to use only the sealing material 405 or the sealing material 406. In addition, the inner sealing material 406 can be mixed with a desiccant, allowing moisture to be absorbed, increasing reliability.

When parts of the pad 412, the first electrode 401 and the auxiliary electrode 402 are extended to the outside of the sealing materials 405 and 406, the extended parts can serve as external input terminals. An IC chip 420 mounted via a converter or the like may be provided on the external input terminals.

As described above, since the lighting device described in this embodiment includes the light emitting element described in Embodiments 1 and 2, the lighting device may be a low power consumption lighting device. Furthermore, the lighting device can be a lighting device with a low drive voltage. Furthermore, the lighting device can be a lighting device with high reliability.

Embodiment 5

In this embodiment, examples of electronic devices each including the light emitting element described in Embodiments 1 and 2 will be described. The light-emitting element described in Embodiments 1 and 2 has high emission efficiency and reduced power consumption. As a result, the electronic device described in this embodiment can each have a light-emitting region with reduced power consumption. In addition, since the light emitting element described in Embodiments 1 and 2 has a low driving voltage, the electronic device can be operated at a low voltage.

Examples of the electronic device to which the above light-emitting element is applied include televisions (also called TVs or television receivers), monitors for computers and the like, cameras such as digital cameras and digital video cameras, digital photo frames, mobile phones (also called cell phones or mobile phones). ), portable game consoles, portable information terminals, audio playback devices, large gaming devices such as pachinko machines or the like. Specific examples of these electronic devices are given below.

9A shows an example of a television. In this television, a display area 7103 is integrated into a housing 7101. In addition, the housing 7101 is supported by a stand 7105. Images can be displayed on the display area 7103, and in the light-emitting area 7103, the light-emitting elements described in Embodiments 1 and 2 are arranged in a matrix. The light-emitting elements can have high emission efficiency. Furthermore, the light-emitting elements can be operated at low voltage. Furthermore, the light-emitting elements can have a long service life. Therefore, the television including the display portion 7103 used using the light emitting elements can be a television with reduced power consumption. Furthermore, the television can be a television with high reliability.

The television can be operated using a control button on the 7101 housing or a separate 7110 remote control. The channels and volume can be controlled using the control buttons 7109 of the remote control 7110 and images shown on the display area 7103 can be controlled. Furthermore, the remote control 7110 can be provided with a display area 7107 to display the data output by the remote control 7110.

It should be noted that the TV is provided with a receiver, a modem and the like. Using the receiver, general television broadcasting can be received. Furthermore, if the TV is connected to a communication network with or without lines via the modem, it can be one-way (from a transmitter to a receiver) or two-way (between a transmitter and a receiver or between receivers) information communication can be carried out.

9B1 illustrates a computer including a main body 7201, a case 7202, a display area 7203, a keyboard 7204, an external connection port 7205, a pointing device 7206 and the like. It should be noted that this computer is manufactured using the light-emitting elements arranged in a matrix in the display area 7203, the light-emitting elements being the same as those described in Embodiment 2 or 3. The Indian 9B1 Computer shown can be a in 9B2 have the structure shown. The Indian 9B2 The computer shown is designed with a second display area 7210 instead of the keyboard 7204 and the pointing device 7206. The second display area 7210 is a touch screen and the input can be carried out by operating the display for input on the second display area 7210 using a finger or a corresponding stylus. The second display area 7210 can also display images other than the input mask. The display area 7203 can also be a touchscreen. The connection of the two screens via a joint serves for protection; e.g. B. can prevent the screens from breaking or cracking while the computer is being stored or carried. The light-emitting elements can have high emission efficiency. Therefore, this computer with the display portion 7203 made using the light emitting elements consumes less power.

9C shows a portable game console with two housings, a housing 7301 and a housing 7302, which are connected via a joint area 7303 so that the portable game console can be closed and opened. The housing 7301 includes a display area 7304 containing the light-emitting elements described in Embodiments 1 and 2 arranged in a matrix, and the housing 7302 includes a display area 7305. In addition, the portable game console included in 9C is shown, a speaker section 7306, a recording medium insertion section 7307, an LED lamp 7308, input means (an operation button 7309, a connection terminal 7310, a sensor 7311 (a sensor with a function of force, displacement, position, speed, acceleration, angular velocity, rotation frequency, distance, light, fluid, magnetism, temperature, chemical substance, noise, time, hardness, electric field, current, voltage, electric power, radiation, flow rate, humidity, gradient, oscillation, smell or infrared rays) and a microphone 7312) and the like. Needless to say, the structure of the portable game console is not limited to the above as long as the display area including the light-emitting elements described in Embodiments 1 and 2 and arranged in a matrix is at least for the display area 7304 or the display area 7305 or both is used and the structure may contain other elements if desired. The portable game console, which in 9C is shown, has a function of reading out a program or values which are stored on a storage medium in order to display them on the display area, and a function of exchanging information with other portable game consoles through wireless communication. It should be noted that the features of the portable game console, which in 9C is shown are not limited to this and the portable game console can have various functions. Since the light-emitting elements used in the display area 7304 have a high emission efficiency, the portable game console containing the above-described display area 7304 can be a portable game console with reduced power consumption. Since the light emitting elements used in the display area 7304 can be operated at low voltage, the portable game console can be a low drive voltage portable game console. Furthermore, since the light-emitting elements used in the display area 7304 have a long service life, the portable game console can be very reliable.

9D shows an example of a mobile phone. The mobile telephone is provided with a display area 7402 built into a housing 7401, operation buttons 7403, an external connection port 7404, a speaker 7405, a microphone 7406 and the like. It should be noted that the mobile telephone 7400 has the display area 7402, which contains the light-emitting elements described in Embodiments 1 and 2 and arranged in a matrix. The light-emitting elements can have high emission efficiency. Furthermore, the light-emitting elements can be operated at a low voltage. Furthermore, the light-emitting elements can have a long service life. Therefore, the mobile phone including the display area 7402 formed using the light emitting elements can be a mobile phone with reduced power consumption. Furthermore, the mobile phone can have a mobile phone be low control voltage. Furthermore, the mobile telephone can be a mobile telephone with high reliability.

If the display area 7402 of the mobile phone, which is in 9D is shown, is touched with a finger or the like, data can be entered into the mobile phone. In this case, operations such as making a call or generating an email can be performed by touching the display area 7402 with a finger or the like.

There are mainly three screen modes of the display area 7402. The first mode is a display mode, which is mainly used to display an image. The second mode is an input mode, which is mainly used to enter information such as letters. The third mode is a display and input mode in which the two modes of the display mode and the input mode are combined with each other.

For example, in the case of making a call or generating an e-mail, a letter input mode that can mainly input letters is selected for the display area 7402 so that the letters are displayed on a screen can be entered. In this case, it is preferred to display a keyboard or number buttons on almost the entire screen of the display area 7402.

If a detection device including a tilt detection sensor such as a gyroscope or an acceleration sensor is provided inside the mobile phone, the display on the screen of the display area 7402 can be automatically changed by determining the orientation of the mobile phone (whether the mobile phone is held horizontally or vertically in landscape or lengthwise format).

The screen modes are changed by touching the display area 7402 or by operating the control button 7403 of the housing 7401. The screen modes can be changed depending on the type of images displayed on the display area 7402. If e.g. For example, if a signal of an image displayed on the display area is a signal of film data, the screen mode is switched to the display mode. If the signal is text, the screen mode switches to input mode.

Furthermore, in input mode, when input by touching the display area 7402 is not performed for a certain period of time while a signal from an optical sensor in the display area 7402 is detected, the screen mode can be controlled to change from the input mode to the display mode is switched.

The display area 7402 can serve as an image sensor. For example, the image of a palm print, a fingerprint, or the like can be captured by touching the display area 7402 with the palm or finger, whereby personal authentication can be performed. By further providing backlighting or a scanning light source that emits near-infrared light in the display area, an image of a finger vein, a hand vein, or the like can be captured.

The structure described in this embodiment may be combined with any structures described in Embodiments 1 to 4 as appropriate.

As described above, the application range of the light-emitting device having the light-emitting element described in Embodiments 1 and 2 is so wide that the light-emitting device can be applied to electronic devices in a variety of fields. By using the light emitting element described in Embodiments 1 and 2, an electronic device with reduced power consumption can be obtained.

10 provides an example of a liquid crystal display device that uses the light emitting element described in Embodiments 1 and 2 as a backlight. In the 10 Liquid crystal display device shown includes a case 910, a liquid crystal layer 902, a backlight unit 903 and a case 904. The liquid crystal layer 902 is connected to a driver IC 905. The light emission described in embodiments 1 and 2 The resulting element is used as a backlight unit 903, to which power is supplied through a terminal 906.

The light emitting element used in Embodiments 1 and 2 is used as the backlight of the liquid crystal display device, therefore the backlight can have reduced power consumption. In addition, the use of the light emitting element described in Embodiment 2 makes it possible to manufacture a planar emission lighting device and further a planar emission lighting device with a larger area, therefore the backlight can be a backlight with a larger area and the liquid crystal display device can be a device with a be a large area. Further, the light emitting device using the light emitting element described in Embodiment 2 can be thinner than a conventional one; therefore, the display device can also be made thinner.

11 Fig. 12 illustrates an example in which the light emitting element described in Embodiments 1 and 2 is used as a table lamp, which is a lighting device. The table lamp, which in 11 1, includes a housing 2001 and a light source 2002, and the light emitting device described in Embodiment 4 is used as the light source 2002.

12 shows an example in which the light emitting element described in Embodiments 1 and 2 is used as an indoor lighting device 3001 and a display device 3002. Since the light emitting element described in Embodiments 1 and 2 has reduced power consumption, a lighting device with reduced power consumption can be obtained. Further, since the light emitting element described in Embodiments 1 and 2 can have a large area, the light emitting element can be used for a large area lighting device. Further, since the light emitting element described in Embodiments 1 and 2 is thin, the light emitting element can be used for a lighting device with a reduced thickness.

The light-emitting element described in Embodiments 1 and 2 can also be used as an automobile windshield or automobile dashboard. 13 1 shows a mode in which the light emitting elements described in Embodiment 2 are used as an automobile windshield and an automobile dashboard. Displays 5000 to 5005 each include the light-emitting elements described in Embodiments 1 and 2.

The display 5000 and the display 5001 are display devices provided in the automobile windshield and in which the light emitting elements described in Embodiments 1 and 2 are installed. The light-emitting element described in Embodiments 1 and 2 can be formed into a so-called see-through display device through which the opposite side can be seen by including a first electrode and a second electrode formed of electrodes having light-transmissive properties. Such see-through display devices can even be provided in the windshield of a vehicle without obstructing visibility. It should be noted that in the case where a transistor for driving is provided, a transistor having a light-transmitting property, such as an organic transistor using an organic semiconductor material or a transistor using an oxide semiconductor, is preferably used.

The display 5002 is a display device which is provided in a column area and in which the light emitting elements described in Embodiments 1 and 2 are installed. The display 5002 can compensate for the obstructed view by the pillar area by displaying an image captured by an image unit provided in the vehicle body. Similarly, the display 5003 provided in the dashboard can compensate for a view obstructed by the vehicle body by displaying an image captured by an image unit provided on the outside of the vehicle body, thereby avoiding blind areas and improving safety. Displaying an image to compensate for an area that the driver cannot see allows the driver to confirm safety easily and conveniently.

The display 5004 and display 5005 can provide a variety of types of information, such as navigation data, a speedometer, a speedometer, an odometer, a fuel gauge, a shift point indicator, and air conditioning setting. The content or layout of the display can be freely changed by a user as appropriate. It should be noted that the information can also be presented by displays 5000 to 5003. Displays 5000 to 5005 can also be used as lighting devices.

The light-emitting element described in Embodiments 1 and 2 can have higher emission efficiency and lower power consumption. Therefore, the load on the battery is low even when a large number of screens such as the 5000 and 5005 displays are provided, thereby enabling comfortable use. For this reason, the light-emitting device and the lighting device each containing the light-emitting element in Embodiments 1 and 2 can be suitably used as a vehicle interior light and an in-vehicle light-emitting device.

14A and 14B show an example of a foldable tablet terminal. 14A shows the tablet terminal, which is not folded. The tablet terminal includes a housing 9630, a display area 9631a, a display area 9631b, a display mode switch 9034, an on/off switch 9035, a power saving switch 9036, a shutter 9033 and an operation switch 9038. It should be noted that in the tablet -Terminal, one or both of the display areas 9631a and the display area 9631b is formed using a light-emitting device containing the light-emitting element described in Embodiments 1 and 2.

Part of the display area 9631a may be a touchscreen area 9632a and input can be made therein when an illustrated control button 9637 is touched. Although only half of the display area 9631a has a display function and the other half has a touch screen function, an embodiment of the present invention is not limited to this structure. The entire display area 9631a can have a touchscreen function. For example, a keyboard may be displayed on the entire area of the display area 9631a so that the display area 9631a is used as a touch screen; therefore, the display area 9631b can be used as a display screen.

Similar to the display area 9631a, a portion of the display area 9631b may be a touchscreen area 9632b. When a switch button 9639 for showing/hiding a keyboard on the touch screen is touched with a finger, a stylus or the like, the keyboard can be displayed on the display area 9631b.

Touch input can be performed in the touchscreen area 9632a and the touchscreen area 9632b simultaneously.

The display mode switch 9034 can switch the display between vertical view, horizontal view and the like and between a monochrome display and color display. The power saving switch 9036 can control the display brightness according to the amount of external light when using the tablet terminal, which is determined by an optical sensor built into the tablet terminal. Another detection device includes a sensor for detecting tilt, such as a gyroscope or an acceleration sensor, may be built into the tablet terminal, in addition to the optical sensor.

Although 14A illustrates an example in which the display area 9631a and the display area 9631b have the same display area, an embodiment of the present invention is not limited to the example. The display area 9631a and the display area 9631b can have different display areas and different display qualities. For example, higher resolution images may be displayed on either of the display areas 9631a and 9631b.

14B shows the tablet terminal, which is folded up. The tablet terminal in this embodiment includes the case 6930, a solar cell 6933, a charge and discharge control circuit 9634, a battery 9635 and a DC-to-DC converter 9636. As an example, shows 14B the charge and discharge control circuit 9634, including the battery 9635 and the DC-to-DC converter 9636.

Because the tablet terminal is foldable, the 9630 case can be closed when the tablet terminal is not in use. As a result, the display area 9631a and the display area 9631b can be protected, thereby providing a tablet terminal with high durability and high reliability for long-term use.

The tablet terminal, which is in the 14A and 14B is shown may have other functions, such as a function to display various types of data (e.g. an image, a movie and a text), a function to display a calendar, a date, the time or the like on the display area, a function to to operate or edit the data displayed in the display area by touch and a function to control the processing by various types of software (programs).

The solar cell 9633 provided on a surface of the tablet terminal can supply power to the touch screen, the display area, a video signal processing area, or the like. It should be noted that the solar cell 9633 may be provided on one or both surfaces of the housing 9630 so that the battery 9635 is efficiently charged.

The structure and operation of the charge and discharge control circuit 9634, which in 14B is shown with reference to a block diagram in 14C explained. 14C shows the solar cell 9633, the battery 9635, the DC-to-DC converter 9636, a converter 9638, switches SW1 to SW3 and the display area 9631. The battery 9635, the DC-to-DC converter 9636, the converter 9638 and the switches SW1 to SW3 correspond to the charge and discharge control circuit 9634, which is in the 14B is shown.

First, an example of operation in the case where power is generated from the solar cell 9633 using external light will be described. The voltage of the current generated by the solar cell is increased or decreased by the DC-to-DC converter 9636 to achieve the voltage necessary to charge the battery 9635. Subsequently, when power from the solar cell 9633 is used to operate the display area 9631, the switch SW1 is turned on and the voltage of the power is increased or decreased by the converter 9638 so that the voltage required for the display area 9631 is achieved. When no images are displayed on the display area 9631, the switch SW1 is turned off and the switch SW2 is turned on so that the battery 9635 is charged.

Although the solar cell 9633 is described as an example of power generation, power generation is not limited thereto, and the battery 9635 may be charged by another power generation means such as a piezoelectric element or a thermoelectric conversion element (Peltier element). The battery 9635 may be charged by a non-contact power transmission module capable of performing charging by wirelessly transmitting and receiving power (without contact), or by any other charging means used in combination, and the power generating means need not necessarily be provided become.

An embodiment of the present invention is not applicable to a tablet terminal with the in the 14A until 14C shown form is limited as long as the display area 9631 is included.

example 1

In this example, a method of manufacturing a light emitting element according to an embodiment of the present invention described in Embodiment 1 and Embodiment 2 and its characteristics will be described. The structural formulas of the organic compounds used in this example are shown below.

A method of manufacturing the light-emitting element of this example will be described below.

First, a film of indium tin oxide containing silicon oxide (ITSO) was formed on a glass substrate by a sputtering method, so that the first electrode 101 was formed. The thickness of this was 110 nm and the electrode area was 2 mm x 2 mm. Here, the first electrode 101 is an electrode serving as an anode of the light-emitting element.

Subsequently, as a pretreatment for forming the light-emitting element on the substrate, UV-ozone treatment was carried out for 370 seconds after washing a surface of the substrate with water and heating the substrate at 200°C for one hour.

Thereafter, the substrate was transferred to a vacuum steamer in which the pressure was reduced to about 10 ^-4 Pa and heated in vacuum at 170 ° C for 30 minutes in a heating chamber of the vacuum steamer, and then the substrate was heated for about 30 minutes cooled down.

Subsequently, the substrate on which the first electrode 101 was formed was attached to a substrate holder provided in the vacuum evaporation device such that the surface on which the first electrode 101 was formed was directed downward. The pressure in the vacuum evaporator was reduced to approximately 10 ^-4 Pa. Subsequently, on the first electrode 101, 4,4',4"-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation: DBT3P-II), represented by the structural formula (i), and molybdenum( VI)oxide was deposited by co-evaporation by an evaporation method using resistance heating, so that the hole injection layer 111 was formed. The thickness of the holein jection layer 111 was adjusted to 33 nm, and the weight ratio of DBT3P-II to molybdenum oxide was adjusted to 4:2. It should be noted that the co-evaporation process is an evaporation process in which a variety of different substances are simultaneously evaporated from the various evaporation sources in a treatment chamber.

Subsequently, a film of 4-penyl-4'-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP) represented by the structural formula (ii) with a thickness of 20 nm was formed on the hole injection layer 111 to form the hole transport layer 112 to form.

Furthermore, on the hole transport layer 112, 2-[3-(Dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTPDBq-II), which is represented by the structural formula (iii), 4-phenyl- 4'-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBA1BP), which is represented by structural formula (iv), and bis[2-(6-tert-butyl-4-pyrimidinyl-κN3 )phenyl-κC](2,4-pentanedionato-κ ² O,O')iridium(III) (Abbreviation: Ir(tBuppm) ₂ (acac)), which is represented by the structural formula (v), by co-evaporation deposited with a thickness of 20 nm, with a mass ratio of 2mDBTPDBq-II to PCBA1BP and Ir(tBuppm) ₂ (acac) being 0.8:0.2:0.05, so that the first light emitting layer 113a was formed; subsequently, 2mDBTPDBq-II and bis(2,3,5-triphenylpyrazinato)(dipivaloylmethanato)iridium(III) (abbreviation: Ir(tppr) ₂ (dpm)), which is represented by the structural formula (vi), were prepared by co-evaporation was deposited with a thickness of 20 nm, with a mass ratio of 2mDBTPDBq-II to Ir(tppr) ₂ (dpm) being 1:0.06, so that the second light-emitting layer 113b was formed. It should be noted that 2mDBTPDBq-II, which is a host material, and PCBA1BP form an exciplex.

Then, the electron transport layer 114 was formed on the light emitting layer 113 in such a manner that a 15 nm thick film of 2mDBTPDBq-II was formed and a 15 nm thick film of bathophenanthroline (abbreviation: BPhen) represented by the structural formula (vii) is represented, was formed.

After forming the electron transport layer 114, lithium fluoride (LiF) was deposited by evaporation to a thickness of 1 nm so that an electron injection layer 115 was formed.

Finally, aluminum was deposited by vapor deposition to a thickness of 200 nm to form the second electrode 102, which served as a cathode. In this way, a light emitting element 1 was manufactured in this example.

It should be noted that in all of the above evaporation steps, the evaporation was carried out by a resistance heating method.

Table 1 shows an element structure of the light-emitting element 1 obtained as described above. [Table 1] Hole injection layer Hole transport layer Light-emitting layer Electron transport layer Electron injection layer First light-emitting layer Second light-emitting layer DBT3P-II: MoO _x BPAFLP 2mDBTPDBq-II:PCBA1BP: Ir(tBuppm)2(aca c) 2mDBTPDBq-II:Ir(tppr) ₂ (dpm ) 2mDBTPDBq-II Bphen LiF 4:2 20 nm 0.8:0.2:0.05 1:0.06 15 nm 15 nm 1 nm 33 nm 20 nm 20 nm

The light emitting element 1 was sealed using a glass substrate in a glove box, the glove box containing a nitrogen atmosphere so as not to be exposed to air (specifically, a sealing material was applied to an outer edge of the element and a heat treatment at 80 °C for 1 hour at the time of sealing).

In the light-emitting element 1, Ir(tBuppm) ₂ (acac) and Ir(tppr) ₂ (dpm) were used as the first phosphorescent compound 113Da and the second phosphorescent compound 113Db. Here, a relationship between a PL spectrum of Ir(tBuppm) ₂ (acac) and ε(λ)λ ⁴ of Ir(tppr) ₂ (dpm) is described. It should be noted that λ indicates a wavelength and ε(λ) indicates a molar absorption coefficient.

20A shows curves of the molar absorption coefficient ε(λ) and ε(λ,)λ ⁴ of Ir(tppr) ₂ (dpm). While the molar absorption coefficient ε(λ) did not show a prominent peak in a region on a longer wavelength side, the curve of ε(λ,)λ ⁴ shows a peak containing a local maximum value at 543 nm. This peak shows the triplet MLCT absorption of Ir(tppr) ₂ (dpm). If this peak overlaps with an emission peak of the first phosphorescent compound 113Da, the energy transfer efficiency can be significantly increased.

20B shows the PL spectrum F(λ) of Ir(tBuppm) ₂ (acac), which is the first phosphorescent compound 113Da, and the curve of ε(λ)λ ⁴ of Ir(tppr) ₂ (dpm), which is the second phosphorescent compound is 113Db. It is clear from the curve that a band with a peak of the PL spectrum F(λ) of Ir(tBuppm) ₂ (acac) is clearly related to the band with the peak on the longest wavelength side of ε(λ)λ ⁴ of Ir(tppr) ₂ (dpm) overlaps, indicating that the combination enables extremely efficient energy transfer. Furthermore, Ir(tBuppm) ₂ (acac), which is the first phosphorescent compound 113Da, has an emission peak at 546 nm, and the spectrum showing ε(λ)λ ⁴ of Ir(tppr) ₂ (dpm), which the second phosphorescent compound is 113Db, has a local maximum on the longer wavelength side at 543 nm, so the difference is 3 nm. The wavelengths 546 nm and 543 nm correspond to 2.27 eV and 2.28 eV, so the difference is 0.01 eV, which is less than 0.2 eV; therefore, the positions of the peaks also suggest the occurrence of efficient energy transfer.

Next shows 21A the molar absorption coefficient curves ε(λ) and ε(λ,)λ ⁴ of Ir(tBuppm) ₂ (acac), which is the first phosphorescent compound 113Da. While a peak in a region on the longer wavelength side has a lower intensity than a peak on the shorter wavelength side of the molar absorption coefficient curve ε(λ), the curve of ε(λ)λ ⁴ has a peak with a high Intensity at 494 nm. The peak exhibiting this peak shows triplet MLCT absorption of Ir(tBuppm) ₂ (acac). If this peak overlaps with an emission peak from an energy donor, the energy transfer efficiency can be significantly increased.

Here, in the light-emitting element 1 in this example, 2mDBTPDBq-II, which is the first host material, and PCBA1BP, which is the first organic compound, form the exciplex 113Ec, and energy is transferred from the exciplex 113Ec to the first phosphorescent compound 113Da. 23 shows the PL spectra of 2mDBTPDBq-II, PCBA1BP, and a mixed film of these (a mass ratio of 2mDBTPDBq-II to PCBA1BP is 0.8:0.2), and it is clear that 2mDBTPDBq-II and PCBA1BP, which is the first organic compound that formed Exciplex 113Ec. 21B shows a PL spectrum F(λ) of the exciplex and the curve of ε(λ)λ ⁴ of Ir(tBuppm) ₂ (acac) phosphorescent compound 113Da. It is clear from the curve that a band with a peak of the PL spectrum F(λ) of the exciplex with the band with the peak on the longest wavelength side of ε(λ)λ ⁴ of Ir(tBuppm) ₂ (acac) overlaps, indicating that the combination enables efficient energy transfer. Furthermore, the PL spectrum of the exciplex has a peak at 519 nm, and the spectrum that is ε(λ)λ ⁴ of Ir(tBuppm) ₂ (acac), which is the first phosphorescent compound 113Da, has a local maximum on the longer wavelength side at 494 nm, so the difference is 25 nm. The wavelengths 519 nm and 494 nm converted into energy correspond to 2.39 eV and 2.51 eV, so the difference is 0.12 eV, which is less than 0.2 eV; therefore, the positions of the peaks also suggest the occurrence of efficient energy transfer.

It should be noted that how out 23 It becomes clear that the PL spectrum of 2mDBTPDBq-II, which is the first host material 113Ha, has a peak at 426 nm, which, converted into energy, corresponds to 2.91 eV. Furthermore, the PL spectrum of PCBA1 BP, which is the first organic compound 113A, has a peak at 405 nm, which converted into energy corresponds to 3.06 eV. The spectrum showing ε(λ,)λ ⁴ of Ir(tBuppm) ₂ (acac) has a peak on the longer wavelength side at 494 nm, which converted to energy corresponds to 2.51 eV. Therefore, the difference with 2mDBTPDBq-II, which is the first host material 113Ha, is 0.4 eV and the difference with PCBA1BP, which is the first organic compound 113A, is 0.55 eV, each exceeding 0.2 eV; therefore, energy is not immediately transferred from 2mDBTPDBq-II or PCBA1BP to Ir(tBuppm) ₂ (acac).

22 shows the PL spectrum F(λ) of the exciplex, the PL spectrum F(λ) of Ir(tBuppm) ₂ (acac), a PL spectrum F(λ) of Ir(tppr) ₂ (dpm), ε( λ)λ ⁴ from Ir(tBuppm) ₂ (acac) and ε(λ,)λ ⁴ from Ir(tppr) ₂ (dpm). It can be seen that energy is ^gradually transferred (around a peak A) first from the exciplex to Ir(tBuppm) _{2 (} acac) and then using the overlap between the PL spectrum of Ir(tBuppm) ₂ (acac) and ε(λ,)λ ⁴ of Ir(tppr) ₂ (dpm) (around a peak B) of Ir( tBuppm) ₂ (acac) is transferred to Ir(tppr) ₂ (dpm). It should be noted that direct energy transfer from the exciplex to Ir(tppr) ₂ (dpm), which is the second phosphorescent compound, is also possible. The reason for this is that like 22 becomes clear, ε(λ)λ ⁴ of Ir(tppr) ₂ (dpm) also with the PL spectrum F(λ) of the exciplex on a shorter wavelength side of the triplet MLCT absorption band (around peak B) of Ir(tppr ) ₂ (dpm) overlaps.

The elemental properties of the light-emitting element were measured. It should be noted that the measurement was carried out at room temperature (in an atmosphere maintained at 25 °C).

15 shows the luminance-current efficiency properties of the light-emitting element 1. In 15 the horizontal axis represents the luminance (cd/m ² ), and the vertical axis represents the current efficiency (cd/A). 16 shows the voltage-luminance characteristics. In 16 the horizontal axis indicates the voltage (V) and the vertical axis indicates the luminance (cd/m ² ). 17 shows the luminance-external quantum efficiency properties. In 17 , the horizontal axis represents the luminance (cd/m ² ) and the vertical axis represents the external quantum efficiency (%). 18 shows the luminance-power efficiency characteristics. In 18 , the horizontal axis represents the luminance (cd/m ² ) and the vertical axis represents the power efficiency (Im/w).

From the above, it was found that the light-emitting element 1 had excellent element properties. In particular, the light-emitting element, as shown in FIGS 15 , 17 and 18 As is clear, it had an extremely high emission efficiency and had a high external quantum efficiency of not less than 20% and a practical luminance of approximately (1000 cd/m ² ). In addition, the current efficiency was about 60 cd/A and the power efficiency was about 60 Im/W, which are excellent values.

19 showed an emission spectrum of the light-emitting element 1 obtained when flowing in the light-emitting element 1. In 19 the horizontal axis indicates a wavelength (nm) and the vertical axis indicates the light emission intensity (arbitrary unit). 19 It can be seen that the light-emitting element 1 shows a light emission spectrum including light having a wavelength in a green wavelength range emitted by bis[2-(6-tert-butyl-4-pyrimidinyl-κN3)phenyl-κC](2,4- pentanedionato-κ ² O,O')iridium(III) (abbreviation: Ir(tBuppm) ₂ (acac)), and light with a wavelength in a red wavelength range that comes from bis(2,3,5-triphenylpyrazinato)( dipivaloylmethanato)iridium(III) (abbreviation: Ir(tppr) ₂ (dpm)) comes from, in a good balance.

From the above, it is clear that the light-emitting element 1, which was an embodiment of the present invention, had a high emission efficiency and provided light from two kinds of emission center substances in a good balance.

Example 2

In this example, a method of manufacturing a light-emitting element corresponding to an embodiment described in Embodiment 1 and Embodiment 2 and the characteristics thereof will be described. The structural formulas of the organic compounds used in this example are shown below.

A method of manufacturing the light-emitting element of this example will be described below.

First, a film of indium tin oxide containing silicon oxide (ITSO) was formed on a glass substrate by a sputtering method, so that the first electrode 101 was formed. The thickness of this was 110 nm and the electrode area was 2 mm x 2 mm. Here, the first electrode 101 is an electrode serving as an anode of the light-emitting element.

Subsequently, as a pretreatment for forming the light-emitting element on the substrate, UV-ozone treatment was carried out for 370 seconds after washing a surface of the substrate with water and heating the substrate at 200°C for one hour.

Thereafter, the substrate was transferred to a vacuum steamer in which the pressure was reduced to about 10 ^-4 Pa and heated in vacuum at 170 ° C for 30 minutes in a heating chamber of the vacuum steamer, and then the substrate was heated for about 30 minutes cooled down.

Subsequently, the substrate on which the first electrode 101 was formed was attached to a substrate holder provided in the vacuum evaporation device such that the surface on which the first electrode 101 was formed was directed downward. The pressure in the vacuum steamer was reduced to approximately 10 ^-4 Pa. Subsequently, on the first electrode 101, 3-[4-(9-phenanthryl)-phenyl]-9-phenyl-9/7-carbazole (abbreviation: PCPPn), represented by the structural formula (viii), and molybdenum (VI) oxide was deposited by co-evaporation by an evaporation method using resistance heating, so that the hole injection layer 111 was formed. The thickness of the lochin jection layer 111 was adjusted to 33.3 nm, and the weight ratio of PCPPn to molybdenum oxide was adjusted to 1:0.5. It should be noted that the co-evaporation process is an evaporation process in which a variety of different substances are simultaneously evaporated from the various evaporation sources in a treatment chamber.

Subsequently, a film of 4-penyl-4'-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP) represented by the structural formula (ii) with a thickness of 20 nm was formed on the hole injection layer 111 to form the hole transport layer 112 to form.

Furthermore, 2-[3'-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTBPDBq-II), which is represented by the structural formula (ix), was formed on the hole transport layer 112 , 4,4'-Di(1-naphthyl)-4"-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBNBB), which is represented by the structural formula (x), and Bis[2 -(6-tert-butyl-4-pyrimidinyl-κN3)phenyl-κC](2,4-pentanedionato-κ ² O,O')iridium(III) (abbreviation: Ir(tBuppm) ₂ (acac)), which represented by the structural formula (v), deposited by co-evaporation with a thickness of 20 nm, the mass ratio of 2mDBTBPDBq-II to PCBNBB and Ir(tBuppm) ₂ (acac) being 0.8:0.2:0.06 , so that the first light emitting layer 113a was formed; then 2mDBTBPDBq-II and bis(2,3,5-triphenylpyrazinato)(dipivaloylmethanato)iridium(III) (abbreviation: Ir(tppr) ₂ (dpm)) which was formed by the Structural formula (vi) is shown, deposited by co-evaporation with a thickness of 20 nm, a mass ratio of 2mDBTBPDBq-II to Ir(tppr) ₂ (dpm) being 1:0.06, so that the second light-emitting layer 113b is formed became. It should be noted that 2mDBTBPDBq-II, which is a host material, and PCBNBB form an exciplex.

Then, the electron transport layer 114 was formed on the light emitting layer 113 in such a manner that a 15 nm thick film of 2mDBTPDBq-II was formed and a 15 nm thick film of bathophenanthroline (abbreviation: BPhen) represented by the structural formula (vii) is represented, was formed.

After forming the electron transport layer 114, lithium fluoride (LiF) was deposited by evaporation to a thickness of 1 nm so that an electron injection layer 115 was formed.

Finally, aluminum was deposited by vapor deposition to a thickness of 200 nm to form the second electrode 102, which served as a cathode. In this way, a light emitting element 2 was manufactured in this example.

It should be noted that in all of the above evaporation steps, the evaporation was carried out by a resistance heating method.

Table 2 shows an element structure of the light-emitting element 1 obtained as described above. [Table 2] Hole injection layer Hole transport layer Light-emitting layer Electron transport layer Electron injection layer First light-emitting layer Second light-emitting layer PCPPn: MoO _x BPAFLP 2mDBTPDBq-II:PCBNBB: Ir(tBuppm) ₂ (aca c) 2mDBTPDBq-Il:Ir(tppr) ₂ (dpm ) 2mDBTPDBq-II Bphen LiF 4:2 20 nm 0.8:0.2:0.06 1:0.06 15 nm 15 nm 1 nm 33 nm 20 nm 20 nm

The light-emitting element 2 was sealed using a glass substrate in a glove compartment, the glove compartment containing a nitrogen atmosphere so as not to be exposed to air (specifically, a sealing material was applied to an outer edge of the element and a heat treatment at 80 ° C for 1 hour at the time of sealing).

In the light-emitting element 2, Ir(tBuppm) ₂ (acac) and Ir(tppr) ₂ (dpm) were used as the first phosphorescent compound 113Da and the second phosphorescent compound 113Db. Here, the relationship between a PL spectrum of Ir(tBuppm) ₂ (acac) and ε(λ)λ ⁴ of Ir(tppr) ₂ (dpm) is the same as in the case of the light emitting element 1, and the description is not repeated. It will be based on description regarding the 20A and 20B referred to in Example 1. Accordingly, it is considered that energy transfer occurs efficiently between the first phosphorescent compound 113Da and the second phosphorescent compound 113Db in the light emitting element 2.

The elemental properties of the light-emitting element were measured. It should be noted that the measurement was carried out at room temperature (in an atmosphere maintained at 25 °C).

24 shows the luminance-current efficiency properties of the light-emitting element 2. 25 shows the voltage-luminance characteristics. 26 shows the luminance-external quantum efficiency properties. 27 shows the luminance-power efficiency characteristics.

From the above, it is seen that the light-emitting element 2 has excellent element properties. Like in particular from the 24 , 26 and 27 As is clear, the light-emitting element has a high emission efficiency and a high external quantum efficiency of not less than 20% at an approximately practical luminance (1000 cd/m ² ). In addition, the current efficiency was about 60 cd/A and the power efficiency was about 60 Im/W, which are excellent values

28 shows an emission spectrum of the light-emitting element 2 obtained when a current of 0.1 mA flowed through the light-emitting element 1. 28 shows that the light-emitting element exhibits an emission spectrum including light having a wavelength in a green wavelength range, which is derived from bis[2-(6-tert-butyl-4-pyrimidinyl-κN3)phenyl-κC](2,4-pentanedionato- κ ² O,O')iridium(III) (abbreviation: Ir(tBuppm) ₂ (acac)), and light with a wavelength in a red wavelength range, which comes from bis(2,3,5-triphenylpyrazinato)(dipivaloylmethanato) iridium(III) (abbreviation: Ir(tppr) ₂ (dpm)) comes from, in a good balance.

Furthermore shows 29 the results of a reliability study under conditions in which the initial luminance of 5000 cd/m ² was assumed to be 100% and the current density was constant. How out 29 As is clear, regardless of the reliability test at the initial luminance of 5000 cd/m ² , the light-emitting element 2 maintained 96% of the initial luminance after 70 hours had elapsed, thereby showing that the light-emitting element had high reliability.

From the above, it is clear that the light-emitting element 2, which was an embodiment of the present invention, had high emission efficiency and provided light from two kinds of emission center substances in a good balance. The light-emitting element was also shown to have high reliability and long service life.

Example 3

In this example, a method of manufacturing a light-emitting element corresponding to an embodiment described in Embodiment 1 and Embodiment 2 and the characteristics thereof will be described. The structural formulas of the organic compounds used in this example are shown below.

A method of manufacturing the light-emitting element of this example will be described below.

First, a film of indium tin oxide containing silicon oxide (ITSO) was formed on a glass substrate by a sputtering method, so that the first electrode 101 was formed. The thickness of this was 110 nm and the electrode area was 2 mm x 2 mm. Here, the first electrode 101 is an electrode serving as an anode of the light-emitting element.

Subsequently, as a pretreatment for forming the light-emitting element on the substrate, UV-ozone treatment was carried out for 370 seconds after washing a surface of the substrate with water and heating the substrate at 200°C for one hour.

Thereafter, the substrate was transferred to a vacuum steamer in which the pressure was reduced to about 10 ^-4 Pa and heated in vacuum at 170 ° C for 30 minutes in a heating chamber of the vacuum steamer, and then the substrate was heated for about 30 minutes cooled down.

Subsequently, the substrate on which the first electrode 101 was formed was attached to a substrate holder provided in the vacuum vapor device such that the surface on which the first electrode 101 was formed was directed downward. The pressure in the vacuum evaporator was reduced to approximately 10 ^-4 Pa. Subsequently, on the first electrode 101, 4,4',4"-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation: DBT3P-II), represented by the structural formula (i), and molybdenum( VI)oxide was deposited by co-evaporation by an evaporation method using resistance heating, so that the hole injection layer 111 was formed. The thickness of the hole injection layer 111 was set to 40 nm, and the weight ratio of DBT3P-II to molybdenum oxide was set to 4:2. It should be noted that the co-evaporation process is an evaporation process in which a variety of different substances are simultaneously evaporated from the various evaporation sources in a treatment chamber.

Subsequently, a film of 4,4',4"-tri(N-carbazolyl)triphenylamine (abbreviation: TCTA) represented by the structural formula (xi) with a thickness of 10 nm was formed on the hole injection layer 111 to form the hole transport layer 112 form.

Furthermore, on the hole transport layer 112, TCTA and bis(2,3,5-triphenylpyrazinato)(dipivaloylmethanato)iridium(III) (abbreviation: Ir(tppr) ₂ (dpm)), which is represented by the structural formula (vi), were carried out Co-evaporated to a thickness of 10 nm, with a mass ratio of TCTA to Bis Ir(tppr) ₂ (dpm) being 1:0.1, so that the second light emitting layer 113b was formed; subsequently, 2-[3-(Dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTPDBq-II), which is represented by the structural formula (iii), was 4-phenyl-4'-(9 -phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBA1BP), which was represented by structural formula (iv), and bis[2-(6-fert-butyl-4-pyrimidinyl-κN3)phenyl-κC] (2,4-pentanedionato-κ ² O,O')iridium(III) (Abbreviation: Ir(tBuppm) ₂ (acac)), which is represented by the structural formula (v), by co-evaporation with a thickness of 5 nm, with a mass ratio of 2mDBTPDBq-II to PCBA1BP and Ir(tBuppm) ₂ (acac) being 0.8:0.2:0.05, so that the first light-emitting layer 113a was formed. It should be noted that 2mDBTPDBq-II, which is a host material, and PCBA1BP form an exciplex.

Then, the electron transport layer 114 was formed on the light emitting layer 113 in such a manner that 2mDBTPDBq-II and Ir(tBuppm) ₂ (acac) were deposited by co-evaporation to a thickness of 20 nm, with a mass ratio of 2mDBTPDBq-II to Ir(tBuppm) ₂ (acac) was 1:0.05, a 10 nm thick film of 2mDBTPDBq-II was formed, and a 20 nm thick film of bathophenanthroline (abbreviation: BPhen), which was represented by the structural formula ( vii) is represented, was formed.

After forming the electron transport layer 114, lithium fluoride (LiF) was deposited by evaporation to a thickness of 1 nm so that an electron injection layer 115 was formed.

Finally, aluminum was deposited by vapor deposition to a thickness of 200 nm to form the second electrode 102, which served as a cathode. In this way, a light emitting element 3 was manufactured in this example.

It should be noted that in all of the above evaporation steps, the evaporation was carried out by a resistance heating method.

Table 3 shows an element structure of the light-emitting element 3 obtained as described above. The materials of the hole transport layer and the second host material of the light-emitting element 3 are significantly different from those of the light-emitting element 1 and the light-emitting element 2. In addition, there are also large differences in the positions of the light-emitting element 3 first and second light-emitting layers with respect to the electrode and the structure of the electron transport layer. [Table 3] Hole injection layer Hole transport layer Light-emitting layer Electron transport layer Electron injection layer First light-emitting layer Second light-emitting layer DBT3P-I I: MoOx TCTA TCTA:Ir(tppr) ₂ (d pm) 2mDBTPDBq-II:PCBA1BP: Ir(tBuppm)2(a cac) 2mDBTPDBq-II: Ir(tBuppm) ₂ (aca c) 2mDBT PDBq-II Bphen 15 nm LiF 4:2 10 nm 1:0.1 0.8:0.2:0.05 0.8:0.05 10 nm 1 nm 33 nm 10 nm 5 nm 20 nm

The light-emitting element 3 was sealed using a glass substrate in a glove compartment, the glove compartment containing a nitrogen atmosphere so as not to be exposed to air (specifically, a sealing material was applied to an outer edge of the element and a heat treatment at 80 ° C for 1 hour at the time of sealing).

In the light-emitting element 3, as in the light-emitting element 1, Ir(tBuppm) ₂ (acac) and Ir(tppr) ₂ (dpm) were used as the first phosphorescent compound 113Da and the second phosphorescent compound 113Db. Here, the relationship between a PL spectrum of Ir(tBuppm) ₂ (acac) and ε(λ)λ ⁴ of Ir(tppr) ₂ (dpm) is the same as in the case of the light emitting element 1, and the description is not repeated. It will be based on description regarding the 20A and 20B referred to in Example 1. Accordingly, it is considered that energy transfer occurs efficiently between the first phosphorescent compound 113Da and the second phosphorescent compound 113Db in the light emitting element 3.

The elemental properties of the light-emitting element were measured. It should be noted that the measurement was carried out at room temperature (in an atmosphere maintained at 25 °C).

30 shows the luminance-current efficiency properties of the light-emitting element 3. 31 shows the voltage-luminance characteristics. 32 shows the luminance-external quantum efficiency properties. 33 shows the luminance-power efficiency characteristics.

From the above, it can be seen that the light-emitting element 3 has excellent element properties. Like in particular from the 30 , 32 and Fig. 237, the light-emitting element has a high emission efficiency and a high external quantum efficiency of not less than 20% at an approximately practical luminance (1000 cd/m ² ). In addition, the current efficiency was about 60 cd/A and the power efficiency was about 60 Im/W, which are excellent values

34 shows an emission spectrum of the light-emitting element 3 obtained when a current of 0.1 mA flowed through the light-emitting element 3. 34 shows that the light-emitting element exhibits an emission spectrum including light having a wavelength in a green wavelength range, which is derived from bis[2-(6-tert-butyl-4-pyrimidinyl-κN3)phenyl-κC](2,4-pentanedionato- κ ² O,O')iridium(III) (abbreviation: Ir(tBuppm) ₂ (acac)), and light with a wavelength in a red wavelength range, which comes from bis(2,3,5-triphenylpyrazinato)(dipivaloylmethanato) iridium(III) (abbreviation: Ir(tppr) ₂ (dpm)) comes from, in a good balance.

From the above, it is clear that the light-emitting element 3, which was an embodiment of the present invention, had a high emission efficiency and provided light from two kinds of emission center substances in a good balance, although the host material was different from that in the light-emitting elements 1 and 2 used difference.

Example 4

In this example, a method of manufacturing a light-emitting element corresponding to an embodiment described in Embodiment 1 and Embodiment 2 and its characteristics have been described. The structural formulas of the organic compounds used in this example are shown below.

A method of manufacturing the light-emitting element (a light-emitting element 4 and a light-emitting element 5) of this example will be described below.

First, a film of indium tin oxide containing silicon oxide (ITSO) was formed on a glass substrate by a sputtering method, so that the first electrode 101 was formed. The thickness of this was 110 nm and the electrode area was 2 mm x 2 mm. Here, the first electrode 101 is an electrode serving as an anode of the light-emitting element.

Subsequently, as a pretreatment for forming the light-emitting element on the substrate, UV-ozone treatment was carried out for 370 seconds after washing a surface of the substrate with water and heating the substrate at 200°C for one hour.

Thereafter, the substrate was transferred to a vacuum steamer in which the pressure was reduced to about 10 ^-4 Pa and heated in vacuum at 170 ° C for 30 minutes in a heating chamber of the vacuum steamer, and then the substrate was heated for about 30 minutes cooled down.

Subsequently, the substrate on which the first electrode 101 was formed was attached to a substrate holder provided in the vacuum vapor device such that the surface on which the first electrode 101 was formed was directed downward. The pressure in the vacuum evaporator was reduced to approximately 10 ^-4 Pa. Subsequently, 4-phenyl-4'-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP), represented by the structural formula (ii), and molybdenum (VI) oxide were deposited on the first electrode 101 by co-evaporation deposited by a vapor deposition method using resistance heating so that the hole injection layer 111 was formed. The thickness of the hole injection layer 111 was set to 33.3 nm, and the weight ratio of BPAFLP to molybdenum oxide was set to 1:0.5. It should be noted that the co-evaporation process is an evaporation process in which a variety of different substances are simultaneously evaporated from the various evaporation sources in a treatment chamber.

Subsequently, a film BPAFLP with a thickness of 20 nm was formed on the hole injection layer 111 to form the hole transport layer 112.

Furthermore, on the hole transport layer 112, 2-[3-(Dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTPDBq-II), represented by the structural formula (iii), 4-phenyl-4' -(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBA1BP), represented by structural formula (iv), and bis[2-(6-tert-butyl-4-pyrimidinyl-κN3)phenyl-κC ](2,4-pentanedionato-κ ² O,O')iridium(III) (Abbreviation: Ir(tBuppm) ₂ (acac)), represented by structural formula (v), by co-evaporation with a thickness of 20 nm deposited, with a mass ratio of 2mDBTPDBq-II to PCBA1BP and Ir(tBuppm) ₂ (acac) being 0.8:0.2:0.06, so that the first light-emitting layer 113a was formed; subsequently, 2mDBTPDBq-II and bis{4,6-dimethyl-2-[3-(3,5-dimethylphenyl)-5-phenyl-2-pyrazinyl-κN]phenyl-κC}(2,6-dimethyl-3 ,5-heptanedionato-κ ² O,O')iridium(III) (Abbreviation: [Ir(dmdppr-P) ₂ (dibm)]), represented by the structural formula (xii), by co-evaporation with a thickness of 20 nm was deposited, with a mass ratio of 2mDBTPDBq-II to [lr(dmdppr-P) ₂ (dibm)] being 1:0.06, so that the second light-emitting layer 113b was formed. It should be noted that 2mDBTPDBq-II, which is a host material, and PCBA1 BP form an exciplex.

Then, the electron transport layer 114 was formed on the light emitting layer 113 in such a manner that a 15 nm thick film of 2mDBTPDBq-II was formed and a 15 nm thick film of bathophenanthroline (abbreviation: BPhen) represented by the structural formula (vii) is represented, was formed.

After forming the electron transport layer 114, lithium fluoride (LiF) was deposited by evaporation to a thickness of 1 nm so that an electron injection layer 115 was formed.

Finally, aluminum was deposited by vapor deposition to a thickness of 200 nm to form the second electrode 102, which served as a cathode. In this way, a light-emitting element 4 was manufactured in this example.

The light-emitting element 5 was manufactured in the same manner as the light-emitting element 4, except that the first light-emitting layer 113a was used instead of [Ir(tBuppm) ₂ (acac)] Tris[2-(6-tert-butyl- 4-pyrimidinyl-κN3)phenyl-κC]iridium(III) (abbreviation: [Ir(tBuppm) ₃ )]), which is represented by structural formula (xiii), was used.

It should be noted that in all of the above evaporation steps, the evaporation was carried out by a resistance heating method.

Tables 4 and 5 show element structures of the light-emitting elements 4 and 5 obtained as described above. [Table 4] Hole injection layer Hole transport layer Light-emitting layer Electron transport layer Electron injection layer First light-emitting layer Second light-emitting layer BPAFLP: MoOx BPAFLP 2mDBTPDBq-II:PCBA1BP: Ir(tBuppm) ₂ (aca c) 2mDBTPDBq-II: Ir(tppr) ₂ (dpm ) 2mDBTPDBq-II Bphen LiF 4:2 20 nm 0.8:0.2:0.06 1:0.06 15 nm 15 nm 1 nm 33 nm 20 nm 20 nm [Table 5] Hole injection layer Hole transport layer Light-emitting layer Electron transport layer Electron injection layer First light-emitting layer Second light-emitting layer BPAFLP: MoOx BPAFLP 2mDBTPDBq-II:PCBA1BP: Ir(tBuppm) ₂ (aca c) 2mDBTPDBq-II: Ir(tppr) ₂ (dpm ) 2mDBTPDBq-II Bphen LiF 4:2 20 nm 0.8:0.2:0.06 1:0.06 15 nm 15 nm 1 nm 33 nm 20 nm 20 nm

The light-emitting elements 4 and 5 were sealed using a glass substrate in a glove compartment, the glove compartment containing a nitrogen atmosphere so as not to be exposed to air (specifically, a sealing material was applied to an outer edge of the element and a heat treatment at 80 ° C for 1 hour at the time of sealing).

In the light-emitting element 4, Ir(tBuppm) ₂ (acac) and [lr(dmdppr-P) ₂ (dibm)] were used as the first phosphorescent compound 113Da and the second phosphorescent compound 113Db. Here, a relationship between a PL spectrum of Ir(tBuppm) ₂ (acac) and ε(λ)λ ⁴ of [lr(dmdppr-P) ₂ (dibm)] is described. It should be noted that λ indicates a wavelength and ε(λ) indicates a molar absorption coefficient. 45A shows curves of the molar absorption coefficient ε(λ) and ε(λ)λ ⁴ of [Ir(dmdppr-P) ₂ (dibm)], which is the second phosphorescent compound 113Db in the light-emitting element 4. While the molar absorption coefficient ε(λ) does not have a clear peak in a region on a longer wavelength side, the curve of ε(λ)λ ⁴ has a peak containing a local maximum value at 509 nm and shoulders at approximately 550 nm and 605 nm on. This peak shows triplet MLCT absorption of [Ir(dmdppr-P) ₂ (dibm)]. If this peak overlaps with an emission peak of the first phosphorescent compound 113Da, the energy transfer efficiency can be significantly increased.

45B shows the PL spectrum F(λ) of Ir(tBuppm) ₂ (acac), which is the first phosphorescent compound 113Da in the light-emitting element 4, and the curve of ε(λ)λ ⁴ of [Ir(dmdppr-P) ₂ (dibm)], which is the second phosphorescent compound 113Db. As is clear from the curve, a band with a peak of the PL spectrum F(λ) of Ir(tBuppm) ₂ (acac) clearly overlaps with the band with the peak on the longest wavelength side of ε(λ)λ ⁴ of [Ir(dmdppr-P) ₂ (dibm)], indicating that the combination enables extremely efficient energy transfer. Furthermore, Ir(tBuppm) ₂ (acac), which is the first phosphorescent compound 113Da, has an emission peak at 546 nm, and the spectrum which is ε(λ)λ ⁴ of [lr(dmdppr-P) ₂ (dibm) ], which is the second phosphorescent compound 113Db, has a local maximum on the longer wavelength side at 509 nm, so the difference is 37 nm. The wavelengths 546 nm and 509 nm correspond to 2.27 eV and 2.44 eV, so the difference is 0.17 eV, which is less than 0.2 eV; therefore, the positions of the peaks also indicate the occurrence of efficient energy transfer. It should be noted that although the peak on the longer wavelength side (peak C) in the spectrum showing ε(λ)λ ⁴ of [lr(dmdppr-P) ₂ (dibm)] is hardly related to the spectrum F(λ) of Ir(tBuppm) ₂ (acac), the band containing peak C in the spectrum which ε(λ)λ ⁴ of [lr(dmdppr-P) ₂ (dibm)] has a broad shape on the side of the longer wavelength, and the spectrum has a clear overlap with the emission spectrum F(λ) of Ir(tBuppm) ₂ (acac) on the longer wavelength side. As a result, efficient energy transfer is achieved.

In the light-emitting element 4, 2mDBTPDBq-II, which is the first host material, and PCBA1 BP, which is the first organic compound, form an exciplex so that energy is efficiently transferred to Ir(tBuppm) ₂ (acac), which is the first phosphorescent compound 113Da is, is transmitted. The relationship is similar to that of the light emitting element 1 and has been described in detail in Example 1, so the description will not be repeated. Reference is made to the corresponding description in Example 1.

46 shows the PL spectrum F(λ) of the exciplex, the PL spectrum F(λ) of Ir(tBuppm) ₂ (acac), a PL spectrum F(λ) of [Ir(dmdppr-P) ₂ (dibm) ], ε(λ)λ ⁴ from Ir(tBuppm) ₂ (acac), and ε(λ)λ ⁴ from [Ir(dmdppr-P) ₂ (dibm)]. It is clear that the energy is gradually transferred from the exciplex to Ir(tBuppm) ₂ (acac) by the overlap between the PL spectrum of the exciplex and ε(λ)λ ⁴ of Ir(tBuppm) ₂ (acac) ( around the peak A) is used, and then from Ir(tBuppm) ₂ (acac) to [Ir(dmdppr-P) ₂ (dibm)] by increasing the overlap between the PL spectrum of Ir(tBuppm) ₂ (acac) and ε(λ)λ ⁴ of [lr(dmdppr-P) ₂ (dibm)] (approximately a range from peak C to 650 nm) is used. It should be noted that direct energy transfer from the exciplex to [Ir(dmdppr-P) ₂ (dibm)], which is the second phosphorescent compound, is also possible. The reason for this is that like 46 becomes clear, ε(λ)λ ⁴ of [lr(dmdppr-P) ₂ (dibm)] also matches the PL spectrum F(λ) of the exciplex in the triplet MLCT absorption band (around peak C) of [lr (dmdppr-P) ₂ (dibm)] overlaps.

In the light-emitting element 5, Ir(tBuppm) ₃ and [lr(dmdppr-P) ₂ (dibm)] were used as the first phosphorescent compound 113Da and the second phosphorescent compound 113Db. Here, a relationship between a PL spectrum of Ir(tBuppm) ₃ and ε(λ)λ ⁴ of [lr(dmdppr-P) ₂ (dibm)] is described. It should be noted that λ indicates a wavelength and ε(λ) indicates a molar absorption coefficient.

47A shows curves of the molar absorption coefficient ε(λ) and ε(λ)λ ⁴ of [lr(dmdppr-P) ₂ (dibm)], which is the second phosphorescent compound 113Db in the light-emitting element 5. While the molar absorption coefficient ε(λ) does not have a clear peak in a region on a longer wavelength side, the curve of ε(λ)λ ⁴ has a peak containing a local maximum value at 509 nm and shoulders at approximately 550 nm and 605 nm on. This peak shows triplet MLCT absorption of [Ir(dmdppr-P) ₂ (dibm)]. If this peak has an overlap with an emission peak of the first phosphorescent compound 113Da, the energy transfer efficiency can be significantly increased.

47B shows the PL spectrum F(λ) of Ir(tBuppm) ₃ , which is the first phosphorescent compound 113Da in the light-emitting element 5, and the curve of ε(λ)λ ⁴ of [Ir(dmdppr-P) ₂ (dibm )], which is the second phosphorescent compound 113Db. It is clear from the curve that a band with a peak of the PL spectrum F(λ) of Ir(tBuppm) ₃ is clearly related to the band with the peak on the longest wavelength side of ε(λ)λ ⁴ of [lr( dmdppr-P) ₂ (dibm)] overlaps, showing that the combination enables extremely efficient energy transfer. Furthermore, Ir(tBuppm) ₃ , which is the first phosphorescent compound 113Da, has an emission peak at 540 nm, and the spectrum which is ε(λ)λ ⁴ of [Ir(dmdppr-P) ₂ (dibm)], which the second phosphorescent compound is 113Db, has a local maximum on the longer wavelength side at 509 nm, so the difference is 31 nm. The wavelengths 540 nm and 509 nm correspond to 2.30 eV and 2.44 eV, so the difference is 0.14 eV, which is less than 0.2 eV; therefore, the positions of the peaks also suggest that efficient energy transfer occurs. It should be noted that although the local maximum on the longer wavelength side (peak C) in the spectrum showing ε(λ)λ ⁴ of [lr(dmdppr-P) ₂ (dibm)] is hardly related to the spectrum F(λ) of Ir(tBuppm) ₃ overlaps, the band containing peak C in the spectrum showing ε(λ)λ ⁴ of [lr(dmdppr-P) ₂ (dibm)] shows a broad shape on the side of the longer wavelength, and that the spectrum on the longer wavelength side has a large overlap with the emission spectrum F(λ) of Ir(tBuppm) ₃ . As a result, extremely efficient energy transfer is achieved.

48A shows the molar absorption coefficient curves ε(λ) and ε(λ)λ ⁴ of Ir(tBuppm) ₃ , which is the first phosphorescent compound 113Da in the light-emitting element 5. The curve of ε(λ)λ ⁴ has peaks with high intensities at 409 nm and 465 nm and a peak containing a shoulder at 494 nm. This peak shows triplet MLCT absorption of Ir(tBuppm) ₃ . If this peak overlaps with a peak of an energy donor, energy transfer efficiency can be significantly increased.

Here, in the light-emitting element 5 in this example, 2mDBTPDBq-II, which is the first host material, and PCBA1BP, which is the first organic compound, form the exciplex 113Ec, and energy is transferred from the exciplex 113Ec to the first phosphorescent compound 113Da. 23 shows PL spectra of 2mDBTPDBq-II, PCBA1BP and a mixed film of these (a mass ratio of 2mDBTPDBq-II to PCBA1BP is 0.8:0.2), and it is clear that 2mDBTPDBq-II and PCBA1BP, which is the first organic compound is, form the Exciplex 113Ec. 48B shows a PL spectrum F(λ) of the exciplex and the curve of ε(λ)λ ⁴ of Ir(tBuppm) ₃ , which is the first phosphorescent compound 113Da. The curve shows that a part of a wavelength range in which a band with a peak of the PL spectrum F(λ) of the exciplex has half the intensity of the peak, the overlaps a part of the wavelength range in which a band with the peak on the longest wavelength side of ε(λ)λ ⁴ of Ir(tBuppm) ₃ has half the intensity of the peak, showing that the combination enables efficient energy transfer .

49 shows the PL spectrum F(λ) of the exciplex, the PL spectrum F(λ) of Ir(tBuppm) ₃ , a PL spectrum F(λ) of [Ir(dmdppr-P) ₂ (dibm)], ε (λ)λ ⁴ from Ir(tBuppm) ₃ , and ε(λ)λ ⁴ from [Ir(dmdppr-P) ₂ (dibm)]. It is clear that the energy is gradually transferred first from the exciplex to Ir(tBuppm) ₃ by the overlap between the PL spectrum of the exciplex and ε(λ)λ ⁴ of Ir(tBuppm) ₃ (around peak A ) is used, and then from Ir(tBuppm) ₃ to [Ir(dmdppr-P) ₂ (dibm)] by calculating the overlap between the PL spectrum of Ir(tBuppm) ₃ and ε(λ)λ ⁴ of [lr (dmdppr-P) ₂ (dibm)] (a range from peak C to 650 nm) is used. It should be noted that direct energy transfer from the exciplex to [Ir(dmdppr-P) ₂ (dibm)], which is the second phosphorescent compound, is also possible. The reason for this is as seen in the 49 becomes clear, ε(λ)λ ⁴ of [lr(dmdppr-P) ₂ (dibm)] also matches the PL spectrum F(λ) of the exciplex in the triplet MLCT absorption band (around peak C) of [lr (dmdppr-P) ₂ (dibm)] overlaps.

The elemental properties of the light-emitting element were measured. It should be noted that the measurement was carried out at room temperature (in an atmosphere maintained at 25 °C).

35 shows the luminance-current efficiency properties of the light-emitting element 4. 36 shows the voltage-luminance characteristics. 37 shows the luminance-external quantum efficiency properties. 38 shows the luminance-power efficiency characteristics.

From the above, it was found that the light-emitting element 4 had excellent element properties. In particular will be made from 35 , 37 and 38 It is clear that the light-emitting element has extremely high emission efficiency and has a high external quantum efficiency of not less than 20% at a practical luminance (1000 cd/m ² ). In addition, the current efficiency was about 50 cd/A and the conduction efficiency was about 50 Im/W, which were excellent values.

39 shows an emission spectrum of the light-emitting element 4 obtained when a current of 0.1 mA flowed through the light-emitting element. In 39 , the horizontal axis indicates a wavelength (nm) and the vertical axis indicates a light emission intensity (arbitrary unit). 39 indicates that the light-emitting element 4 shows an emission spectrum including light having a wavelength in a green wavelength region coming from [Ir(tBuppm) ₂ (acac)] and light having a wavelength in a red wavelength region coming from [lr (dmdppr-P) ₂ (dibm)] comes from, in a good balance.

40 shows the luminance-current efficiency properties of the light-emitting element 5. 41 shows the voltage-luminance characteristics. 42 shows the luminance-external quantum efficiency properties. Fig.438 shows the luminance power efficiency characteristics.

From the above, it was found that the light-emitting element 5 had excellent element properties. In particular will be made from 40 , 42 and 43 It is clear that the light-emitting element has extremely high emission efficiency and has a high external quantum efficiency of not less than 25% at a practical luminance (1000 cd/m ² ). In addition, the current efficiency was about 65 cd/A and the conduction efficiency was about 70 Im/W, which were excellent values.

44 shows an emission spectrum of the light-emitting element 5 obtained when a current of 0.1 mA flowed through the light-emitting element 5. In 44 , the horizontal axis indicates a wavelength (nm) and the vertical axis indicates a light emission intensity (arbitrary unit). 44 indicates that the light-emitting element 5 shows an emission spectrum including light having a wavelength in a green wavelength range coming from [Ir(tBuppm) ₂ (acac)] and light having a wavelength in a red wavelength range coming from [lr (dmdppr-P) ₂ (dibm)] comes from, in a good balance.

From the above, it is clear that the light-emitting elements 4 and 5, each corresponding to an embodiment of the present invention, had high emission efficiency and provided light from two kinds of emission center substances in a good balance.

Reference example 1

A preparation of the organometallic complex bis[2-(6-tert-butyl-4-pyrimidinyl-κN3)phenyl-κC](2,4-pentanedionato-κ ² O,O')iridium(III) (abbreviation: [Ir( tBuppm) ₂ (acac)]), which is used in the above embodiment, will be described. The structure of [Ir(tBuppm) ₂ (acac)] is shown below.

(Step 1: Preparation of 4-tert-Butyl-6-phenylpyrimidine (Abbreviation: HtBuppm))

First, 22.5 g of 4,4-dimethyl-1-phenylpentane-1,3-dione and 50 g of formamide were placed in a round-bottomed flask equipped with a return tube, and the air in the flask was replaced with nitrogen. This reaction vessel was heated so that the reacted solution was refluxed for 5 hours. This solution was then poured into an aqueous sodium hydroxide solution and an organic layer was extracted with dichloromethane. The obtained organic layer was washed with water and a saturated brine and dried with magnesium sulfate. The solution was filtered after drying. The solvent of this solution was distilled off and the resulting residue was purified by silica gel column chromatography using hexane and ethyl acetate as a flow agent in a volume ratio of 10:1 to obtain a pyrimidine derivative HtBuppm (colorless oily substance, yield 14%). A synthesis scheme of step 1 is shown below.

(Step 2: Preparation of Di-µ-chloro-bis[bis(6-fert-butyl-4-phenylpyrimidinato)iridium(III)] (Abbreviation: [Ir(tBuppm) ₂ Cl] ₂ ))

Subsequently, 15 ml of 2-ethoxyethanol, 5 ml of water, 1.49 g of HtBuppm, which was obtained in step 1, and 1.04 g of iridium chloride hydrate (IrCl ₃ ·H ₂ O) were placed in a round-bottom flask equipped with a return tube. introduced and the air in the flask was replaced with argon. Subsequently, microwave irradiation (2.45 GHz, 100 W) was carried out for 1 hour to achieve a reaction. The solvent was distilled off and the residue obtained was filtered off with suction and added Washed with ethanol to obtain a dinuclear complex [Ir(tBuppm) ₂ Cl] ₂ (yellow-green powder, yield 73%). A synthesis scheme of step 2 is shown below.

(Step 3: Preparation of (Acetylacetonato)bis(6-tert-butyl-4-phenylpyrimidinato)iridium(III) (Abbreviation: [Ir(tBuppm) ₂ (acac)]))

Further, 40 ml of 2-ethoxyethanol, 1.61 g of the dinuclear complex [Ir(tBuppm) ₂ Cl] ₂ obtained in step 2, 0.36 g of acetylacetone and 1.27 g of sodium carbonate were added to a round bottom flask containing equipped with a return tube, and the air in the flask was replaced by argon. Subsequently, microwave irradiation was carried out for 60 minutes to achieve a reaction. The solvent was distilled off and the resulting residue was filtered with ethanol and washed with water and ethanol. This solid was dissolved with dichloromethane and the mixture was filtered through a filter aid filtered, in which Celite (manufactured by Wako Pure Chemical Industries, Ltd., Catalog No. 531-16855), alumina and Celite were stacked in this order. The solvent was distilled off and the resulting solid was mixed with a mixed solvent of dichloromethane and Hexane recrystallized to give the desired substance as a yellow powder (yield 68%). A synthesis scheme of step 3 is shown below.

An analysis result by nuclear magnetic resonance spectroscopy ( ^1H NMR) of the yellow powder obtained in step 3 is described below. The result showed that the organometallic complex Ir(tBuppm) ₂ (acac) was obtained.

^1H NMR. δ (CDCl ₃ ): 1.50 (s, 18H), 1.79 (s, 6H), 5.26 (s, 1H), 6.33 (d, 2H), 6.77 (t, 2H) , 6.85 (t, 2H), 7.70 (d, 2H), 7.76 (s, 2H), 9.02 (s, 2H).

Reference example 2

In this reference example, a preparation of bis{4,6-dimethyl-2-[3-(3,5-dimethylphenyl)-5-phenyl-2-pyrazinyl-κC]phenyl-xC}(2,6-dimethyl-3 ,5-heptanedionato-κ ² O,O')iridium(III) (abbreviation: [Ir(dmdppr-P) ₂ (dibm)]), the iridium complex used in the organometallic in this example, is described. The structure of [lr(dmdppr-P) ₂ (dibm)] (abbreviation) is shown below.

(Step 1: Preparation of 2,3-Bis(3,5-dimethylphenyl)pyrazine (Abbreviation: Hdmdppr))

First, 5.00 g of 2,3-dichloropyrazine, 10.23 g of 3,5-dimethylphenylboronic acid, 7.19 g of sodium carbonate, 0.29 g of bis(triphenylphosphine)palladium(II) dichloride (abbreviation: Pd(PPh ₃ ) ₂ Cl ₂ ), 20 ml of water and 20 ml of acetonitrile were introduced into a round-bottomed flask equipped with a reflux tube, and the air in the flask was replaced with nitrogen. This reaction vessel was subjected to microwave irradiation (2.45 GHz, 100 W) for 60 minutes to be heated. Furthermore, 2.55 g of 3,5-dimethylphenylboronic acid, 1.80 g of sodium carbonate, 0.070 g of Pd(PPh ₃ ) ₂ Cl ₂ , 5 ml of water and 5 ml of acetonitrile and irradiation with microwaves (2.45 GHz, 100 W) were added. was carried out again for 60 minutes for warming.

Water was then added to this solution and the organic layer was extracted with dichloromethane. The obtained organic layer was washed with a saturated aqueous solution of sodium hydrogen, water and a saturated solution of sodium chloride, and was dried with magnesium sulfate. After drying, the solution was filtered. The solvent of the solution was distilled off and the resulting residue was purified by flash column chromatography using hexane and ethyl acetate as a solvent in a ratio of 5:1. The solvent was distilled off and the resulting residue was purified by flash column chromatography using dichloromethane and ethyl acetate as a solvent in a volume ratio of 10:1, so that Hdmdppr (abbreviation), which was the pyrazine derivative to be prepared, as a white powder with a Yield of 44% was obtained. It should be noted that the microwave irradiation was carried out using a microwave system (Discover, manufactured by CEM Corporation). A synthesis scheme of step 1 is shown in (a-1).

(Step 2: Preparation of 2,3-Bis(3,5-dimethylphenyl)-5-phenylpyrazine (Abbreviation: Hdmdppr-P))

First, 4.28 g of Hdmdppr (abbreviation) obtained in step 1 and 80 mL of dry THF were introduced into a 3-neck flask and the air in the flask was replaced with nitrogen. After the flask was cooled with ice, 9.5 ml of phenyllithium (1.9M phenyllithium solution in butyl ether) was added dropwise and the mixture was stirred at room temperature for 23.5 hours. The reacted solution was poured into water and the solution was extracted with chloroform. The obtained organic layer was washed with water and a saturated sodium chloride solution and dried with magnesium sulfate. Manganese oxide was added to the resulting mixture and the mixture was stirred for 30 minutes. The solution was then filtered and the solvent was distilled off. The resulting residue was purified by silica gel column chromatography using dichloromethane as a solvent so that Hdmdppr-P (abbreviation), which was the pyrazine derivative to be prepared, was obtained as an orange oil in a yield of 26%. A synthesis scheme of step 2 is shown in (a-2).

〈Step 3: Preparation of Di-g-chloro-tetrakis{4,6-dimethyl-2-[3-(3,5-dimethylphenyl)-5-phenyl-2-pyrazinyl-κN]phenyl-κC}diiridium(III ) (Abbreviation: [Ir(dmdppr-P) ₂ Cl] ₂ )〉

Then, 15 ml of 2-ethoxyethanol, 5 ml of water, 1.40 g of Hdmdppr-P (abbreviation) obtained in step 2, and 0.51 g of iridium chloride hydrate (IrCl ₃ ·H ₂ O) (manufactured by Sigma-Aldrich Corporation) was introduced into a round bottom flask equipped with a return tube and the air in the flask was replaced with argon. Irradiation with microwaves (2.45 GHz, 100 W) was then carried out for 1 hour. The solvent was distilled off and then the obtained residue was filtered with suction and washed with ethanol to obtain [Ir(dmdppr-P) ₂ Cl] ₂ (abbreviation), which is a dinuclear complex, as a reddish brown powder in a yield of 58% . A synthesis scheme of step 3 is shown in (a-3).

〈Step 4: Preparation of Bis{4,6-dimethyl-2-[3-(3,5-dimethylphenyl)-5-phenyl-2-pyrazinyl-κN]phenyl-κC}(2,6-dimethyl-3, 5-heptanedionato-κ ² O,O')iridium(III) (Abbreviation: [lr(dmdppr-P) ₂ (dibm)])〉

Further, 30 ml of 2-ethoxyethanol, 0.94 g of [Ir(dmdppr-P) ₂ Cl] ₂ , which is the dinuclear complex obtained in step 3, 0.23 g of diisobutyrylmethane (abbreviation: Hdibm) and 0, 52 g of sodium carbonate was introduced into a round bottom flask equipped with a return tube and the air in the flask was replaced with argon. Irradiation with microwaves (2.45 GHz, 120 W) was then carried out for 60 minutes. The solvent was distilled off and the residue obtained was filtered off with suction with ethanol. The obtained solid was washed with water and ethanol and recrystallization was carried out with a mixed solvent of dichloromethane and ethanol so that [lr(dmdppr-P) ₂ (dibm)] (abbreviation), the organometallic complex in an embodiment of the present invention, when a dark red powder was obtained in a yield of 75%. A synthesis scheme of step 4 is shown below in (a-4).

An analysis result by nuclear magnetic resonance spectroscopy ( ^1H NMR) of the dark red powder obtained by the above-described method is described below. The results showed that the organometallic complex [lr(dmdppr-P) ₂ (dibm)] (abbreviation) was obtained in this preparation example.

¹ H NMR, δ(CDCl ₃ ): 0.79 (d, 6H), 0.96 (d, 6H), 1.41 (s, 6H), 1.96 (s, 6H), 2.24 -2.28 (m, 2H), 2.41 (s, 12H), 5.08 (s, 1H), 6.46 (s, 2H), 6.82 (s, 2H), 7.18 ( s, 2H), 7.39-7.50 (m, 10H), 8.03 (d, 4H), 8.76 (s, 2H).

Reference symbols

10: electrode, 11: electrode, 101: first electrode, 102: second electrode, 103: EL layer, 111: hole injection layer, 112: hole transport layer, 113: light-emitting layer, 113a: first light-emitting layer, 113Da: first phosphorescent compound, 113Ha : first host material, 113b: second light-emitting layer, 113Db: second phosphorescent compound, 113Hb: second host material, 113A: first organic compound, 113Ec: exciplex, 114: electron transport layer, 115: electron injection layer, 400: substrate, 401: first electrode, 402: Auxiliary electrode, 403: EL layer, 404: second electrode, 405: sealing material, 406: sealing material, 407: sealing substrate, 412: pad, 420: IC chip, 601: driver circuit area (source line driver circuit), 602: pixel area, 603: driver circuit area ( gateline driver circuit), 604: sealing substrate, 605: sealing material, 607: space, 608: wiring, 609: FPC (Flexible Printed Circuit Board), 610: element substrate, 611: switching TFT, 612: current control TFT, 613: first electrode, 614: Insulator, 616: EL layer, 617: second electrode, 618: light emitting element, 623: n-channel TFT, 624: p-channel TFT, 625: desiccant, 901: housing, 902: liquid crystal layer, 903: backlight unit, 904: Housing, 905: Driver IC, 906: Terminal, 951: Substrate, 952: Electrode, 953: Insulator tion layer, 954: separation layer, 955: EL layer, 956: electrode, 1001: substrate, 1002: base insulation film, 1003: gate insulation film, 1006: gate electrode, 1007: gate electrode, 1008: gate electrode, 1020: first intermediate insulation layer , 1021: second intermediate insulation layer, 1022: electrode, 1024W: first electrode of a light-emitting element, 1024R: first electrode of a light-emitting element, 1024G: first electrode of a light-emitting element, 1024B: first electrode of a light-emitting element, 1025: partition, 1028: EL- Layer, 1029: second electrode of a light-emitting element, 1031: sealing substrate, 1032: sealant, 1033: transparent base material, 1034R: red color layer, 1034G: green color layer, 1034B: blue color layer, 1035: black layer (black matrix), 1036: top layer , 1037: third intermediate insulation film, 1040: pixel area, 1041: driver circuit area, 1042: peripheral area, 1044W: white light emitting area, 1044R: red light emitting area, 1044B: blue light emitting area, 1044G: green light emitting area, 2001: housing , 2002: light source, 3001: lighting device, 3002: display device, 5000: display, 5001: display, 5002: display, 5003: display, 5004: display, 5005: display, 7101: housing, 7103: display area, 7105: stand, 7107 : display area, 7109: control button, 7110: remote control, 7201: main body, 7202: housing, 7203: display area, 7204: keyboard, 7205: external connection port, 7206: pointing device, 7210: second display area, 7301: housing, 7302: housing, 7303 : joint area, 7304: display area, 7305: display area, 7306: speaker area, 7307: recording medium insertion area, 7308: LED lamp, 7309: operation button, 7310: connection terminal, 7311: sensor, 7400: mobile telephone, 7401: housing, 7402: display area, 7403: control button, 7404: external connection port, 7405: speaker, 7406: microphone, 9033: shutter, 9034: switch, 9035: on/off switch, 9036: switch, 9038: control switch, 9630: housing, 9631: display area, 9631a: display area, 9631b: display area, 9632a: touch screen area, 9632b: touch screen area, 9633: solar cell, 9634: charge and discharge control circuit, 9635: battery, 9636: DC-to-DC converter, 9637: operation button, 9638: converter, and 9639: Button.

Claims (9)

A light-emitting element comprising: a first electrode, a first light-emitting layer, a second light-emitting layer, and a second electrode, the first light-emitting layer being disposed between the first electrode and the second light-emitting layer, the second light-emitting layer being disposed between the first light-emitting layer and the second electrode, wherein the first light-emitting layer comprises: a first phosphorescent compound, a first host material, and a first organic compound, wherein the second light-emitting layer comprises: a second phosphorescent compound, and a second host material, wherein the the first host material and the first organic compound are capable of forming an exciplex, wherein the light emitted from the second phosphorescent compound has a longer wavelength than the light emitted from the first phosphorescent compound, a band having a length on the longest wavelength side Peak of a function ε(λ)λ ⁴ of the second phosphorescent compound overlaps with a band having a peak of the phosphorescence spectrum F(λ) of the first phosphorescent compound; where λ denotes a wavelength, and where ε(λ) denotes a molar absorption coefficient at wavelength λ. Light emitting element Claim 1 , in which the first electrode is a cathode and the second electrode is an anode. Light emitting element Claim 1 , in which the first light-emitting layer and the second light-emitting layer are in contact with each other. Light emitting element Claim 1 , in which the first phosphorescent compound has a phosphorescence peak in a range of 500 nm to 600 nm and the second phosphorescent compound has a phosphorescence peak in a range of 600 nm to 700 nm. Light emitting element Claim 1 , in which an emission spectrum of the exciplex overlaps with a peak on the side of the longest wavelength of a function ε(λ)λ ⁴ of the first phosphorescent compound. Lighting device comprising a light-emitting element Claim 1 having. Light-emitting device comprising a light-emitting element Claim 1 and a control unit for controlling the light-emitting element. Display device comprising a light-emitting element Claim 1 in a display area and a control unit for controlling the light-emitting element. Electronic device incorporating a light-emitting element Claim 1 having.

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